now this is extremely off topic, but I was speaking with Lasershock in the gog.com irc (unofficial) and he gave me the idea, but I put it together
http://www.wegame.com/watch/Black_Mesa_Source_Official_Trailer/
Black Mesa source is a Half-Life 2 mod, to recreate the original Half-Life 1 using the source engine, only with updated graphics, level design, and model design, and as a result of those updates, an updated storyline as well.
Now, on topic, I wanted to say how I really appreciate total conversion mods, and how they extend the life of games. Some of my favorite mods for games like half-life are Sven Coop, which allows you to play Half-Life 1 single player, cooperatively as well as custom maps, I also enjoy BrainBread which is a zombie mod.
Many mods, such as Overdose, for Painkiller, get picked up by the original game publisher, and then turned into an actual retail product, which is another item I'm extremely pleased with. Game modifications help not only the gaming community with extra hours of gameplay with a game, but also with providing the developer with new employees and products :)
What are some of your favorite mods, and why? Also feel free to share videos to those mods as well.

Dystopia
As I generaly dislike multiplayer, Dystopia was game that totally sucked me in by advanced cooperation of multiple playable classes both in physical world and in cyberspace. Add fantastic weapons, great leveldesign and a shitload of good ideas and you have IMO the best multiplayer MOD ever released. I'm not playing it now and I don't know how much alive servers are, but I can tell for sure - if some Dystopia servers are up and if enough people are playing it, it's totally worth trying. Sadly, this MOD DEPENDS on community, there's not individualism possible - so when you meet idiotic people, experience goes out of the window - more than in most other MP games, anyway

Freespace 2 has a ridiculously great Mod community. Not only do they have awesome use made campaigns (some with actual voice acting) like Derelict, BluePlanet, and Inferno, but they make stand alone total conversions of the engine so people can play Babylon 5 campaigns (with all the ships and voice actors), and they have an upcoming BattleStar Galactica total conversion as well.
Oblivion and Morrowind have great mods as well. I like hte FCOM mod for Oblivion that combines 4 of the more popular ones (I believe Obscuro's overhaul, Martigens monsters, and a couple others I forget) into one that re-balances the world and adds a crap load of items/armor/creatures.
Counter Strike is a nice mod as well...

I am currently playing Dystopia, and for the (sadly relatively low amount of people) there are more then enough servers always up.
Hopefully, with the release of 1.2 incl. Steamworks, this will change (as in more players not not enough servers for the players..).
Just try it. You can later say how cool you are, as you even played it before everyone did :)
Official V1 trailer:
http://www.youtube.com/watch?v=P6ez9-fGdS0
Also we (speaking of players) are in the process of creating movies/teaser/trailer and even more tutorials for the upcoming 1.2. For official released material, just check out the media gallery on dystopia-game.com.
As for mods in general: I like them, too.
Many mods like Sven Coop etc are really cool, as they add things the original release lacked, like, coop.
And even if i do not like the game itself that much, like Morrowind or Oblivion, it's nice to see people develop mods. So you can choose how to play and so, many fix stuff the one or the other doesn't like and so..
So keep it coming @mod developers out there.

I had given Dystopia a shot, back when they first came out, I was much more into the source modding scene then, but I didn't like it so much thenI might give it another shot later, but right now, my initial impression is so bad, I can't be bothered.

by the way that's an awesome avatar...

Thanks, I actually got it from Xbox.com, have the game on XBLA and just saved the image from my game history.
You can either take it straight from here, or go to my xbox live history and get it there, my gamer tag is Rezoule

It's actually quite interesting how mods have become such a big part of consideration of whether or not to buy one game over another for many people (myself included). Sure, FPS games have always had active communities, but every single genre now gets some fantastic mod work.
For me, I think my favorites have been the mods for the Total War series. Rome : Total War had the dumbest AI I have seen in a strategy game on release...throw in the Europa Barbaorum mod, though, and it's a whole new game. And there are several fantastic mods for MTW2, as well, they really salvaged a lot of the game (Stainless Steel, Deus lo Vult, Broken Crescent, etc,. etc.). Those collectively would be my choice, simply because they salvaged a game that was rather disappointing out of the box.

When I am buying a PC game it is totally a consideration for me. In fact, that is the reason I bought Fallout 3 on the PC. Even without the official construction kit unavailable (At the time I write this) there are already some kick butt mods coming out.
here is a pack from fileplanet with some of the best (so far): Click here
You have to have a file planet account (obviously) but it's worth downloading.

my fallout 3 wishlist:
fix third person so we can stay in it. :)
recreate fallout 1.
make sleeping with a prostitute more rewarding? (doesn't have to be sexual, but 175 caps for that, is laaaaame).
remove level 20 cap so I can get more perks with the same character!

There are already mods that remove the Level 20 Cap, but unless you also use the mod where you can raise your skills higher, you will not be able to finish the level up once you got everything to 100, as you can't spend any skillpoints, and you have to spend all.

Ah, I don't have it for PC, so I can't really complain too much, as I only have the 360 version.

I knew they were suppose to be released, didn't realize they have released them already. I'll have to take a look.
I absolutely love the game and think it is a very valid addition to the fallout franchise. I'm looking forward to see what modders do with it: I know I'm planning something myself.

My biggest issue is the level 20 cap. I'm 42 or 43 hours in and at level 18 and a half. I know I haven't explored near everything; i'd say close to half the map isn't uncovered. (Maybe a little less then half...) The game world is really, really dense.