For me:
X-Com: Interceptor. But that's probably because I'm a whore for space sims - I'm fairly sure it's not a very good game. Just a guilty pleasure of mine.

Company of Heroes; my gutt warned me that it would be horrible since it was an rts and I usually hate them but low and behold its my favortie rts.

UFO: Afterlight - people had not been kind to this game, but I loved it a lot (even though the tactical combat is barely tactical at all).
Far Cry Instincts - I'm a big fan of the original Far Cry, which from what I've seen from other fans should mean that I hate the console version with a passion. I don't. I thought it was great, like an alternate reality version of the game. "What if Far Cry was a linear, scripted shooter?" The two games are like two adaptations of the same novel. The basic ingredients are the same, but the results are totally different.
Metal Gear Solid 2 - me and my brother were both big fans of the first MGS, so when he played MGS2 and said it just became terrible, and would ruin my memories of the first game, this stopped me from playing it for about two years. I'm glad I finally tried it though. While I agree it has major problems, I think it does a lot of things right. It tells a story that could not have worked in any other medium, and that gives it value. It also has my favourite gameplay of the entire series.
Prince of Persia Warrior Within - like everyone else, I was disgusted by the unnecessary tonal switcheroo, and even though I got a free copy of the game I couldn't be bothered playing past the first ten minutes. And nobody ever blamed me for this; I definitely wasn't the only one who had written off the game. But a few years later I decided to give it a chance again, and ended up actually enjoying it despite the constant lame. And the terrible boss battles.
Vivisector - the only information I could find on the game was a rather negative GameFAQs review, but I decided to try the game anyway. I loved it; it was brilliant. I've posted a review on its Gamersgate page to try and spread the love.

Too Human. This is a game that every gaming out let (But 2 that I know of) pretty much panned. Yet I find it is one of the most fun multiplayer games that I have played on the xbox 360 in a long, long time. I honestly get the same feeling I did with diablo 2. I really enjoy the visuals, the story, and the combat.
Forgive me if this is only suppose to be older games ;)

Got this off of GamersGate too; I enjoyed it as well. For some reason GG won't accept my review of it, even though I've submitted it numerous times.
As for games I was warned off of but ended up liking: Blood. A friend of mine used the immortal words "Blood sucks!" to describe it. I decided to try it anyways, and ended up enjoying it very much.
It's weird that my friend didn't like the game, because our tastes in games are pretty similar.

Yeah, my first review got eaten for unknown reasons. But this was actually a good thing, because I discovered that long (i.e. paragraphed) reviews look awful on that site, since the line breaks are removed. Perhaps try writing another, shorter one and see what happens?
Glad I'm not the only person in the world to appreciate the game, though. :]

This is the review I wrote; as you can see it uses up nearly all of the 3,000 characters GamersGate allows for user reviews:
Vivisector is an arcade-styled first-person shooter that is very loosely based on The Island of Doctor Moreau: you play a lowly soldier sent to the tropical island of Isla Sorna to investigate the disappearance of some people, and soon find yourself caught in a battle for survival against enemy soldiers and "humanimals," creatures that are part man and part animal, the results of scientific experiments.
While based on a piece of classic literature, the plot in Vivisector can't hold up to close scrutiny: there are lots of holes and inconsistencies.
Vivisector is best described as Far Cry crossed with Serious Sam: you make your way through open jungle areas and enclosed military and scientific facilities battling enemies, who often attack en masse. The game is very much an arcade shooter in that it allows you carry over a dozen weapons that don't ever need to be reloaded. While most FPS games these days try and be more realistic, Vivisector is happy to relive the old-school run and gun Doom days. There's a bit of an RPG element that allows you to increase your health, armor, and weapon stats, but no one is going to confuse this with Deus Ex.
Vivisector doesn't really do anything new, but it does enough things right to make it enjoyable for FPS fans: there are lots of big guns, lots of enemies to shoot, a few boss battles, and the game is fairly lengthy. The levels are varied and many of them are quite elaborately designed, making them interesting to look at and explore.
Like in Serious Sam and Painkiller, enemies will frequently warp in around you, making you stay on your toes. Annoyingly, the designers often have monsters spawn five feet in front of you or behind you when you cross invisible triggers, which leads to lots of cheap deaths. This more prevalent in the early stages of the game than it is later on, but it's still cheap.
The design of the enemies in Vivisector is quite interesting, with some good-looking animal-human hybrids. The animations on the creatures are good, and the individual monsters contain lots of detail. Vivisector also has a "vivisection" feature that allows you to blow chunks of armor, skin, and flesh off enemies; it's good-looking effect, but it's for appearances only: enemies can keep attacking unhindered even after you've blown all the meat off their bones and have reduced them to little more than walking, gun-toting skeletons. It looks a bit silly.
Technically Vivisector is done well, with good visuals and sound. The graphics aren't cutting-edge, but are solid and detailed, and outside of some hammy voice-acting and generic "battle music" the audio portion of the game is respectable. The game is relatively bug-free too, although a couple of minor errors were encountered.
Like many modern first-person games, Vivisector doesn't have much replay value, and since there's no multiplayer, once you've finished the campaign there's little reason to play the game again. Still, it's a fun enough romp while it lasts.
Here's a gameplay video I made: http://vimeo.com/1292127

That's surprisingly similar to my original review! Yours is better, though.
The only real difference is that I was a bit more positive about the vivisection feature; its ridiculous cartoon silliness was one of my favourite things about the game (but I'm a big fan of living skeletons; have been ever since I saw Jason and the Argonauts). You'll notice I left this bit out of the short version though, because I was worried I made it sound like a gimmick game.
Anyway, two voices speak louder than one - I reckon you should edit that down into a nice bite-sized review and get it up on Gamersgate, even if it is in a compromised form. To be honest, it wouldn't surprise me if Gamersgate just ignore proper reviews (perhaps they suspect plagiarism, or just can't be bothered adding the mark-up), since they seem to be more interested in short semi-literate blurbs than in-depth analyses.
And now we should probably stop hijacking this thread. :]

The most recent game I was involved in and which wasn't very great according to the critics was Stubbs The Zombie... man I love zombies, I love this game. :3
I can't rember any older ones... I will try when I'll be at my place: there's ton of game boxes :)

Fallout: Tactics.
When I got this game the first time a friend solid it to me for 10$ a week after he'd bought it for 50$, with a warning that it was a terrible version of Fallout. I tried it with some trepidation, but really enjoyed it..
As a turn based tactical squad combat game, ala Jagged Alliance and X-Com. It isn't a successor to Fallout 2, and that's it's biggest flaw.
Other games I'd been warned about, but were wonderful:
System Shock 2. There's no way to overstate how fun this game is, but I had a friend that hated it. Apparently couldn't get past crude graphics, weapons braking and hard character building choices early on.

you has some crack headed friends, what are they all like 'omg halo is teh win i played teh theme osng on gato hero, and it was pwn. i have 3505050505050505 gamer pts cuz i haz all teh achievements.'??

Quest for Glory V - It's not a bad game really, it's just very different from the others.
It's closer to an RPG with adventure elements - whereas the originals were Sierra adventures with RPG elements. The story and environments weren't as interesting as QFG3 or 4, but I still found it to be a very fun 'fanservice' game.
Arcanum - Not warned from the RPG community, but when it first came out I heard nothing but bad things. It was also called unbalanced and not anything special. No clue why I listen for so long, because I loved it when I finally played it. Of course I used Drog's fan patch, so maybe theres some good in waiting.

Deus Ex: Invisible War - Everyone I knew who had played the first Deus Ex warned me against this one. Having never played the first one, I decided to try it anyway and was very glad I did. After playing IW, I went back and played Deus Ex and I realize now why many of the people didn't like IW, they are practically two unrelated games in terms of style and gameplay. I still think IW was a great game in its own right, it just might not have been a great sequel to a great game.

Thief - The Dark Project
Several people warned me about this one. "Boring," one said. "No fighting; no killing," was another opinion. "Weird setting. Medieval castles with electric lights?"
I got a copy with a graphics card and finally installed it and, after I learned how to stay alive more than 60 seconds (don't try to kill everything--this isn't Quake), I fell in love with it.
Bought Thief 2 (Metal Age), Thief 3 (Deadly Shadows) and, finally, Thief Gold (at a garage sale) rounded out my collection.
The number of fan-made missions is mind-boggling.
If that's not enough, I found out that, once you've played everything, you can take the Thief Editor (DROMED), edit the levels and add all sorts of fun cheats and jokes. My favorite is either my Stealth Blackjack (adds -16384 to your exposure, rendering you invisible) or my Ghoul-Killer Sword (with added heat, damage and holy powers) which will kill any NPC with one or two whacks. You're safe unless they hit you first....