Not entirely sure! I have several:
Super Metrioid, SNES, 1994:
I love games like this and Super Metroid is undoubtly the best of its kind. Epic adventure platformer with great control, customization, and multiple paths, with a killer soundtrack and clean graphics. Nice nice nice.
Shenmue 2, Dreamcast/Xbox, 2001:
Yes, it may be terribly linear and plodding, but I still love it to bits. Shenmue I/II has only just lost out on the title of "highest video game budget ever" comming in at a cool $70 mil, and boy was it worth it. This game has some of the highest production values I've ever seen in anything. The game world is beautifuly crafted, its 80s Hong Kong setting recreated down to the finest detail. There is a full voice over for every single individual in the game (Something that the Shenmue series pioneered), and most importantly, it's just great fun to play, if only once. The virtua fighter-esque combat is great, the detective work is exciting, as are the chases. A truely epic adventure, shame it's just so one-sided.
I own the rare European Dreamcast version, which is in Japanese with subtitles. =3 It goes now for £50 on ebay, which makes me feel special. =p (Though I'd never sell my copy)
LOZ: Occarina or Time, N64, 1998:
What can I say that hasn't already been said about this wonderful game? It's perfect. Once again, shame it's pretty linear. It always sucks when a great game has so little replay value.
Banjo-Kazooie N64, 1998:
IMO, the greatest 3D platformer ever, winning over by far the vastly overrated Mario 64. Its loveable bear and bird duo provided some inovative gameplay, a great variety of moves and tricks, and the levels were well designed and colourful. The graphics were stunning at the time, and still hold up nicely today (As shown by the great XBLA remake). Sure, there was a lot of pointless collecting stuff, but I'm a saidist who likes that sort of thing. Also, above and beyond anything else, it's British! =P
Ufouria, NES 1991:
So very, very few people have played this game, which is a shame because it rocks. It was only released in Japan and PAL regions, so yeah, obscure. It's a adventure platformer in the same vain as Metroid, but designed by people on LSD! The character designs in this game are pretty wacky (point to avatar) and the special attacks wackier. The premise of the game is pretty basic, you've landed on some alien planet and you've got to find all your amnesiac friends, collect 3 keys, and beat a boss at the end, but it's all very thoughtfuly designed, colourful, and at times, downright bizzare. A little on the short side maybe, but great fun to play whilst it lasts.
My gosh that was a self indulgent post! You should seriously play those games, though. Like, now.