Phew...LOTS of games. I'll give a list of what I can remember, but edit this later on if I think of more:
PC:
Leisure suit Larry
Wolfenstein 3D (yes...the ORIGINAL)
doom 1 & 2 (on hardest not-nightmare setting)
descent
heretic
hexen
prince of persia
Commander Keen 4&5
(stunts) (you can't really count it as it is just creating tracks and riding on it...but I managed to constantly beat the best opponent, though).
Freecell, minesweeper, patience (i'm the only one who did this?
)
Super street fighter 2 turbo
Dungeons & Dragons 1&2 (though the first was pretty much a "you have now won the game" without mentioning whatsoever)
secret of monkey island 1 & 2 (best point 'n click adventures EVER!)
King's quest 4 (I got 2 times nearly to the end but was stuck because of some crashing thing...then it turned out it was just one or two things left before the end of the game).
Mortal kombat 1 & 2 (though the difficulty was shit...after 2 or 3 fights, it became almost impossible to do anything until you wasted another continue)
Dune 2
C&C 1, 2, 3 (though halfway tiberian sun, I was just hoping it would get BETTER instead of worse)
Red alert 1, 2, 3
Warcraft 1, 2, 3 (not 100% if I finished warcraft 2, though)
Fallout 1, 2, 3 (the third one is totally different, but fun nonetheless)
Duke Nukem 1&2 (well...I think I did. Can't recall an end boss, though)
Duke Nukem 3D
Abe's Oddyssey
Unreal, unreal: return to na pali
UT (or UT99, if you want to take the series seriously)
(UT2004) (I didn't finish the final boss on principle because it was so weak...but considering I played this for YEARS, I can't not mention it)
UT3 (but GOD, someone please fire the scenario writer...it's so bad it manages to give "camp" a bad name)
Half life
Bioshock
kingdom of looting (okay, it's a browser game without end...but I DID finish the main quest with walkthroughs).
Gameboy monochrome:
Tetris (level 9 high 5)
Super mario land 1,2,3
Bugs Bunny
Double dragon 1 & 2 (perhaps 3 as well...can't remember)
Batman
Bubble bobble (including that alternate levels stuff)
Duck tales 1 (perhaps 2 as well)
Gargoyles quest
Kirby's dream land
Kirby's pinball land
One of the mega mans...can't remember which one
Mystic quest
TMNT 1 & 2
Zelda: link's awakening
Choplifter 2
One of the castlevania's
Mario vs Donkey kong
Hook
Terminator 2
Bart Simpson escape from camp...something
Home alone (perhaps 2 as well...not sure)
NES:
double dragon 2 (though my worst enemy was actually my team mate
)
Arcade (or mame):
Teenage Mutant Ninja turtles 1 & 2
The simpsons
X-men
Vendetta
Asterix (but man...those end bosses are so unfair at the end...I'm glad I played this one mostly on mame)
Penguin brothers (for those who never heard it: try it out...it's an awesome platformer)
A Japanese picture-puzzle game (I later found out it is the same thing as Mario Picross...but with better time management rules).
Pang 1, 2 and 3
Sunset riders
Joe & Mac
Super NES:
Super pang
Super mario world
Final fight 1 & 3 (never found somewhere where they were selling nr. 2)
star fox adventures
Donkey kong country
Secret of mana (I think...it was an RPG, but not a turn-based one)
Jurassic park (I think...I got pretty far in the game, in any case)
Aladdin
gameboy color:
Zelda: oracle of seasons & ages (yay for emulators)
gameboy advance:
Zelda minish cap (on the wii)
PSP:
Puzzle quest: challenge of the warlords (thanks to a correct amount of spell distribution, I beat the final boss - or pretty much everyone - in the first turn).
Gamecube:
Zelda: 4 swords adventure
Wii:
Super Mario Galaxy 1 & 2
Zelda: twilight princess
Super Paper mario
Super Smash Bros Brawl (well...the subspace emissionary...barely bothered playing the actual fighting game)
Warioware: smooth moves (at least: I THINK I unlocked all the minigames)
Wario land: the shake dimension
Guitar hero 3, 4 & 5
(rock band 2) (sorta...I still have one or two songs to finish in the main quest, but I'm too busy rocking out to care)
Sin & punishment 2
House of the dead: overkill (a bit too short, if you ask me)
donkey kong country returns
Kirby's epic yarn (my girlfriend made me do it!)
Kororinpa (again...not 100% sure. and I probably missed a bonus level or two)
(wii fit plus) (okay, this is really an endless game...but as far as unlocking/achieving things go, this one is pretty complete)
(wii sports resort) (ditto)
Wiiware:
World of goo
Ghost mania
...and probably a bunch I forgot (may edit this even later)