Difficult question. While I'd only be able to list about 10 games that I'd consider favorite games of all times narrowing it down to one would be very difficult. I guess at the moment the answer would actually be for a rather young game/game series. PS2 - Smackdown respectively Smackdown vs Raw
Ive played and still own plenty of older PC games one of my all time favorites and prob the only one I ever find myself returning to and playing every few years (besides wing commander ) is Star Craft. Im Amazed that blizzard still supports this great game its fun to jump on battle net every now and then to see how bad I suck at the game.
I also enjoy Xwing Alliance and the dark forces games. Die by the sword and duke nukem is another couple of games Im fond of just don't make me choose
I would have to say my favorite xbox game is that operation flashpoint. I wish the replayabily was as great for other games for the console.
Gotta add space quest I bought the indiviual space quest 4 and space quest 2 had a heck of a time finding the rest until I stumbled upon the space quest collection and was quite happy to find it. Kinda sucks that they never made space quest 7. I enjoyed the good old days of typing adventures I remember not to long ago a fan made space quest was made the lost chapter I think it was called. I loved part three traveling around in the Aluminum Mallard that was prob my favorite of the series but it did get better as years went by. Poor Poor Roger after all those interesting ways to die I didn't think that lack of interest would finally do him in.
Never even heard of advance wars must of missed it.
Outside of WC it would have to be hands down Sam N' Max Hit The Road.
I know all of the puzzles and easters eggs by heart but I still laugh my ass off every time I play. ScummVM runs it really well now too.