I don't play too many DOS games these days (so many games, so little free time). But when in middle and high school, I played quite a
of them. And I mean many dude. So I can do a top twenty five for you from those memories. All of this stuff I played via DOS, no Windows ports here.
Abuse -Very difficult, very unique run 'n gun.
Alien Carnage
-A SNES quality run 'n gun with good level designs.
DOOM
-Well this is obligatory.
F29 Retaliator
-A very fun combat flight simulator with smooth 3D graphics even on a 286.
Gorillas
-This was a demo two player artillery fire game that came with QBASIC, and it's still funner than 90% of the schlock that releases today.
King's Quest IV: The Perils of Rosella-I've beaten most of the KQs (except III, VII, and VIII), but KQIV remains my favorite.
Leisure Suit Larry in the Land of the Lounge Lizards
-A sleazy dude doing sleazy funny things the game.
Liero-Good shareware game where you could split-screen kill your friends as gun toting worms.
LOOM-An amazingly beautiful unique adventure game, extremely highly recommended.
Quake
-If you actually played it when it released (I did), Quake was nothing short of mind blowing; a paradigm shift for the FPS genre.
Quest for Glory II: Trial By Fire-My favorite QFG entry. The Windows VGA remake is probably the way to go today.
Ningyō Tsukai 2 (Metal & Lace 2)
My favorite DOS fighting game, although it's not for everyone due to hentai elements.
Prince of Persia
-This game has been ported to a bajillion platforms. The SNES version is actually the best, but I beat the DOS one first.
Privateer: Righteous Fire
-I never got into Wing Commander much, but I spent many a teenage night exploiting these galaxies.
Rise of the Dragon-A well written cyberpunk murder mystery that's leagues better than the overrated
Snatcher.
Scorched Earth-Super fun artillery fire multiplayer game.
SkyRoads
-Very challenging hover racer with polygonal tracks.
Solar Winds-A short series (The Escape/Galaxy) of shooty space sim games, recommended for fans of Star Control.
Stargoose Warrior
-A rare and quite good shmup.
Space Quest IV: Roger Wilco and the Time Rippers
-This game was hilarious, I need to beat the rest of this series.
Star Wars: Dark Forces
-Of all the FPS that function mechanically similar to DOOM, this is my favorite.
System Shock
-Still the best FPS-RPG hybrid I've experienced, unfortunately it's too complex and cerebral for casual players.
The Adventures of Willy Beamish
-Be a smartass kid and defeat an evil corporation in this incredibly well animated adventure.
The Secret of Monkey Island-One of the very best, and certainly the funniest, adventure games ever made.
Ultima Underworld II: Labyrinth Of Worlds
-An incredibly immersive action-DRPG, nobody makes games this smart anymore.
If anybody wants any extra info on any of those, just say so. I'm probably forgetting some favorites, so I may add more later. There's thousands of DOS games after all!