No-one has yet mentioned the good old LucasArts adventure games, I am willing to let this oversight pass, accepting it as simply due to your uncontrollable rage directed towards the corporation for their cancellation of Sam and Max 2, but I shall nonetheless address this lack. Grim Fandango is possibly my favourite game ever (I can't decide between it and Ocarina of Time/Wind Waker), the noir atmosphere, jazz stylings, dry humour and supreme inventiveness make it the most incredible fun, while Sam and Max and the incredible Monkey Island series are simply hilarious. DoTT's good too, though I feel Full Throttle is somewhat of a weaker link. If you haven't played them, do so. Now.
Currently I'm playing through Deus Ex, and I have to say that it is absolutely superb. The freedom offered and open-ended route to all goals is wonderful, I have been playing through without killing everyone, whilst my friend made it his mission to annihilate almost every single living creature in that virtual world (I worry about him sometimes). Wonderful plot as well, twists and turns and conspiracies lurk around every corner. I'm just entering Bunker III in the Paris Catacombs, but so far Hong Kong has been my favourite map, from Wan Chai to the MJ12 Lab it was a delight to play.