Another vote for KSP. That game is indeed amazing, maybe a bit hard at the beginning but once you get the grasp of the controls it keeps you glued to your chair.
Kerbal denizens have a great charm as well, they're just lovely... Although it's sad how many brave Kerbal astronauts have died during my failed flights.
Fun fact: I happen to know the offices where the developers work since it's pretty close to where I used to work, I was amazed by how small their team is for such a fine piece of software. The tech team is just above 10 guys.
Right now I'm all about League of Legends, but I'm also jumping back and forth between Bioshock and Fallout New Vegas. I dunno why I don't just sit and play them all the way through, maybe I get bored after a bit
Just started playing Tomb Raider 2013, i must say its the best game ever designed. the game is almost 10GB in size and high in terms of graphics with life like display and actions, but still consume very less processor usage and ram. it is addictive.
apart form that, started with battlefield bad company 2 (already done with battlefield 3), NFS most wanted 2012 and GTA IV.
I'm not interested in today's great big blockbusters or MMO's either. I want games to be stress relief, not careers. KSP may be the first non-freeware game I've gotten since Starcraft 1.
