Point and Click adventures:
Beneathe a Steel Sky (1994): This is possibibly the best p&c game Iv'e ever played, it's based upon David Gibbs comic of the same name, set in the industrial future of Austrailia. www.the-underdogs.org has the game files, but you'll need the SCUMM emulator to run it (there's one I have which is directX compatible, great as now I can't even find out what my port, IRQ and DMA channel are)
Day of the Tentacle (1995, also known as DOTT): Yes, this is the best p&c ever. Ones after this failed terribly. Mad doctor makes time machine, his tentacle pets take over the world.
Shoot 'em Up's: (There's some brilliant and mostly japanese ones like R-Type which I'll omit as I have never owned a console, and with the death of the dreamcast probably never will)
Tyrian(1995): Why Epic MegaGames (Yes, what ever happened to the mega in their title?) never made a sequel to this I'll never know. The most intense gun frenzy ever, and with a plausable plot and interesting characters. Look for Tyrian2000 on p2p networks, which is now abandonware.
Raptor:Call of the shadows(1994): This game had more of an RPG feel to it than Tyrian, which is why I liked it so much. Smaller and simpler, but does have an auto tracking vulcan cannon! Yey!
Role Play Games:
Alphaman(1995): Pure ASCII game, comparable to rouge or nethack, but so much better. Personally I can't stand spells and goblins and whatnot, and Alphaman being set in the post apoc setting is much more pleasing.
Fallout(1995?): Yes, this is possibily the best RPG ever. Lots of guns, lots of blood, a realistic level of foul language and atmosphere. Plus the turbo plasma rifle, melty fun! And also featured my favorite '40s era song.
Fallout2(1996 probably): More of the same, and better.
Strategy:
Dune(1991): Cyro did an excellent job capturing the tale and atmosphere of Dune in an enjoyable and sometimes challenging game.
Fallout Tatics (2000 or so): So much fun on a Lan, especially because I find it funny how a supermutant can fire a M2 single handedly.
Real Time Strategy:
Command & Conquer(1994):Simple to edit, and brings back so many happy memories of 486's, LAN parties and Belgian beer. Especially the latter.
Total Annihlation(1997): Even easier to edit and create content for, and the scale of the battles I havent seen scaled scince. That factor alone makes it my favorite RTS of all time except for all the other numerous features, and two sides who wern't black and white. Finding and downloading the game now are extremely hard, and the commander packs (contained the game, all of the expansion packs and loads of other stuff I can't remember. I should have kept the box to) are being auctioned for hundreds of dollars on eBay now.
Other Strategy's:
Master of Orion2(1995):Best Galactic Conquest game ever. Nothing in it's league comes close. Master of Orion 3 by comparison was a disapointment.
Alpha Centurai(1999?):Civ3 came out after this, yet seemed to be regressed. AC was the pinacle of Civ games.
First Person shooters:
Unreal Tournament(1999): This game has it all, fun weapons, good enough music, graphics which still look good today, more mods and maps you should shake a redeemer at, and CTF-Hall Of Giants, my favorite 3d enviroment ever.
UT2004(2004):Vechiles are so much fun! Chatting to team mates leads for great coordination. Online this is my favorite FPS, even better than Halo. And I really liked Halo online.
Farcry(2004): Gorgeous, P90, machete. I am happy.
Other Games:
Sims(1999): Love it or loathe it, there's something really appealing about controlling a group of people.
Streetrod(1989 I think): Fun little RPG/Racing game. Take and modify cars from 1930 to 1970 and race them against others.
Stunts(1990, also known as 4D Racing):A simplistic racing game, but you can make the tracks. Loads and loads of features can be put in.
Lincity(1995 I think): There's a BeOS and Win32 version of this game, and it's great in a complex way. What simcity should have been.