Interesting thread, I like it. Now I'll have to think of a few games that impressed me. Might be a little off topic, but I really enjoyed Geometry Wars for the DS. Very basic graphics, very simple gameplay, but for a 2-D game in a totally 3-D world, I found it to be a title that holds it's own to basically anything out there.

Journey to Silius - NES. Makes very good use of the sound capabilities of the NES.

Tomb Raider - Has already been commented on, but it really pushed the limits with the sheer size of the game, as far as the area you are able to explore.

Twisted - 3DO. Again, maybe a little off topic, but a really intersting concept that has never really been duplicated, at least to my knowledge.

Burgertime - Intellivision. MUCH better port than the NES, which is interesting, because it's not as advanced of a system. As a matter of fact, I think INTV Burgertime is probably the most authentic arcade translation out there. Except the play control, of course.

Sunset Riders - SNES. Again, a very true-to-original arcade port. Hand over fist better than the Genny version. If you ever can compare side-by-side SNES to arcade, it is virtually identical. Makes good use of the technical capabilities of the SNES.

Dragon's Lair/Mad Dog McCree - Arcade. Using Laserdiscs when people had barely heard of CD's? If that is not technically amazing, I don't know what is. Playing either one of those games even today is still impressive. Admittedly, the acting on Mad Dog is weak, but you are literally playing a game in a movie setting. And Dragon's Lair...well, not much needs to be said there.

That's all I got for now, anyways.