I can't decide between Grand Theft Auto IV and the first Mass Effect.
GTA IV, I love for many reasons. It looked incredibly good to me graphically, especially the car destruction, played extremely well (I loved the combat, and the car physics), and you felt like you were in a real, living city, what with all the friend activities and just the atmosphere of the place. The missions were interesting as usual for the GTA series. But what I loved most was the storyline, the way they swapped the usual silly shenanigans for a serious, tragic storyline. And with that, still managing to be as genuinely funny as all the previous games in the series, just in a down-to-earth way. People always say San Andreas was better, but honestly, the only way in which that one beats IV for me is in terms of having a better game-world to explore and more to do after the plot's finished. IV still beats it for me.
As for Mass Effect, it was the first Bioware game I played and still my favourite. Again, I loved the graphics, it was a seriously good-looking game, and the characters were just so interesting to talk to, even the ones that weren't particularly exciting in themselves, because you could control all your interactions with them, and because they were, by and large, very well-written and well-acted. The combat in Mass Effect was certainly nothing special, in fact it's the one area in which I consider the two sequels superior, but there was nothing particularly wrong with it in Mass Effect either; same with the Mako, I never got all the hate. But really what makes it so great to me is just the sheer epicness of the storyline. The climactic battle on the Citadel is completely incredible in every way, and never fails to inspire awe despite the fact I must have completed the game about thirty times by now. Similarly to my other choice, I'm aware a lot of people consider earlier Bioware games like KOTOR to be superior, but while I love KOTOR it never had quite the same level of epic that Mass Effect did for me. I found the combat comparatively dull and the storyline didn't seem so interesting (though it's certainly still the best storyline within the Star Wars universe to me).
