Yeah, the game was a classic back in the Windows 95 days. Problem was, it was too short, and didn't sell well, but now it is a super rare game to own, and it is actually fun, I would pay full price for it!

The Reap!

Only 76 votes!

http://www.gog.com/wishlist/games/the_reap

This is a good, old, game. One of the very good shooters of old, reminds an arcade game and most importantly, feels like a clone of the best games this genre has to offer.

Great sound and effects, especially visual ones; weapons, explosions, this is an eyecandy! A little bit hard. But worth it. I would buy it without second thought. Please gog bring it? Please, people, vote for it?

Here, a gameplay video of it, with intro and first stage goodness:

https://www.youtube.com/watch?v=YN820hQ50NM

Dark Designs Trilogy

Something of a primitive Eye of the Beholder or early Wizardry games. Notable in that they were made by John Carmack in his pre-ID days.

RAILS ACROSS AMERICA (currently 59 votes)

It is very odd that Railroad Tycoon II has more than 1400 votes and this one merely 59. It is one of the best railroad simulation games ever made and is published by Strategy First, so there is no good reason for the game not appearing here (other than lack of votes maybe). The game also covers the 19th century in North America, probably the best setting for a railroad sim. The reception among the critics was quite well, but for some reason Rails Across America never became very popular among the gamers, which makes it by all means an underrated gem. Check out the mobygames page if you wanna have a look!

Vote for it!

<span class="bold">Bermuda Syndrome</span> (146 votes)

It's an amazing platformer similar to games like Another World of Flashback. Just watch this intro! After being mysteriously transported to a different world you have to deal with savage princess and dinosaurs! It's not about running and shooting only, you have to solve many environmental puzzles. Sometimes you have to ask your lovely friend to give you a hand (pushing some buttons etc.). The game has reasonable length and nice gameplay. It's a shame it's not as known as aforementioned classics, it really deserves to be played!

updated the rules and posted a TOP 20 list. Games up to 2005 are now allowed :)

One more update!

1. The vote limit is now 350, since the games between 300-350 votes range also look pretty underrated.
2. New Rule: You can post about a game that is already mentioned.

Pariah (http://www.gog.com/wishlist/games/pariah)

FPS from 2005. Nothing terribly deep or original here, but it looks fine and enjoyable on its own terms. Only 74 votes so far.
MobyGames entry: http://www.mobygames.com/game/windows/pariah

I'll add another one: Offensive

One of the first strategies I played on my own PC. Released in 1996 by Ocean Software. You can play as either Allied or German side, 20 battles each (in fact it's the same battles, so they are pretty balanced).
Isometric view. The graphics were pretty good for that time. What I loved about it was the level of detail put into it. Trees, parks, benches, cars, trains, children playing, people walking... it was pretty neat. You can't save mid-level, you get a passowrd every time you finish one so you can start from that level, but that's not a big issue since the levels are not really long (15-30 mins). Another thing I disliked, was that in missions where you had to destroy all enemies (i.e most of the missions), you had to hunt down every last one, including that 1 infantry unit that's running around in the far corner of the map because of its low morale.

I'm surprised so few people heard about it. No wikipedia entry. No screenshots on mobygames (I attached some here). Its name doesn't help. Usually when the title is a generic word, you can add "video game" to it on google, and you still get good search results. If I search "offensive video game" however, I'd get info about GTA (now Hatred).

Wishlist entry. Only 4 (!) votes so far
http://www.gog.com/wishlist/games/offensive

Could you include my entry now? Or is there something more I should add/edit?

done

Pariah is a pretty solid game for sure, it didn't help the entire gamingpress dismissed it as a Halo clone, ingnoring the truth that Halo didn't do anything original that hadn't been done before.

Take No Prisoners (wishlist entry: http://www.gog.com/wishlist/games/take_no_prisoners)

A post-apocalyptic 3D shooter with a peculiar "top-down" perspective.
It's from 1997 and at this moment it has just 200 votes.
I've never played this game but it looks like it could provide some decent mindless shooting fun (MobyGames entry: http://www.mobygames.com/game/windows/take-no-prisoners)

Done. Unfortunately I made the second post right after the first, so GOG merged the two automatically.
Alright, then... GOG please bring it on!

CASTLES: THE NORTHERN CAMPAIGN (currently 142 votes)

People have been for the expansion almost since GOG's launch with no success. The original game is here, but the expansion is not. The game adds new graphics, economics, new combat features (vikings, archers etc). and troop training. Also, Brian Fargo is credited as the Executive Producer. According to Wikipedia, "Castles: The Northern Campaign was reviewed in 1992 in Dragon #180 by the Lessers. The reviewers gave the game 5 out of 5 stars." So if we have Castles here, why not The Northern Campaign? Check out the [url=http://www.mobygames.com/game/castles-the-northern-campaign/]mobygames page

Vote for it!