The Journeyman Project 2 and 3. I played the first and loved it, but was never able to find the others.

The thief series is something I would like to play, as well as System shock 1.

I'm a huge RPG player and game collector so I managed to acquire most of the classic RPG's...I just haven't finished a lot of them. Mostly because of time. However, I did miss Freespace 2, Starcraft, and the X-Com series. I heard that all are phenominal but I have yet to buy them. Freespace 2 I will get from GOG in the near future.

1 addendum: the Ultima series is one I've never played also.

Diablo 2
Thief 2
Ultima Underground
A game from the gold box series
Marathon
I never played any of the above before and would definitely like to. The games I've played a bit of but never finished (and want to finish or replay), well, that list is way too big.

I'm lucky enough to have had a stepmother that just happened to buy the entire series.. and just so happened to forget when she moved out of the house. >>
I did see this on Amazon though.

The 11th Hour. Loved The 7th Guest, but I never got a chance to play the sequel.

A relatively little known game, but I always wanted to try X-Com Enforcer and to a lesser extent, Interceptor. I always liked the X-com universe but sucked at the games, so these 2 look like a chance to get into it.
Also, Ultima IX: Ascension. Not sure why, never played an Ultima game but this one does still interest me, despite the reputation it had.

I would also like to add the Thief games as an addenum to my short list... If they ever appear here I will snag em

I never got a chance to play Thousand Arms :( i was a big fan of Wild Arms at the time and though Thousand Arms was some sort of sequal (I know its not now) but I always wanted to play it :(

I always wanted to play Persona 2, but I wanted to play the original one first :/

Ōkami, MGS3, ICO, Shadow of Colosus, the Oddworld games on X-box. Well I have never played them because I have NEVER owned a console.

System Shock 1 and 2, I need to play these games! I hear so many good things about them all the time.
Also the theif series looks like a lot of fun, really want to try that out.

Planescape torment, so many great things said about it, so many people reminiscing about how great the story is, and somehow I completely missed the boat.
Oh and Tribes 2, another game I managed to completely miss out on.
/sigh

--Ultima series.
Especially Ultima: Underworld and Ultima IX.
--Grim Fandango.
--Monkey Island series.
--Omikron