Lair - The only hardcore game I have seen that features a Dragon Rider. No less, a Game I've been wanting for the absolute longest time; since I got a 1st gen PS3.
Grand Theft Auto - It's just so surprisingly fun to create absolute havoc and not have to pay a price. Especially since everything is fake; so I don't feel guilty or anything for running over some random guy or capping a cop.
Pokemon - Any mention of this series and you have my attention. For a game oriented towards the younger ages, this can be a pretty intense series if you get deep enough into it. It was the very first game series I ever got into, and it will be the last I get out of (if anything of the sort is to happen).
The Legend of Zelda - I admit I was extremely late to this series. The very first Zelda game I played was Twilight Princess; but it was not to be the last. And now, I've played almost every Zelda game to date (excluding Wind Waker and all the games with "Toon Link").
Metroid - Another series I was late as hell to. Started with Metroid Prime. But since then, I have gone on to play almost every Metroid game out there. Only missed out on Zero Mission, Hunters and Pinball.
Dead Space - The first game in a long time to actually freak me out. Even to watch. Also one of the most intelligent games to date; Silent hill is a close second, but I could easily bear to watch Silent Hill. Dead Space just hits something and scares the hell out of me...
Fallout - My latest game fix, Fallout is addicting beyond measure, especially when you pump up the difficulty. Sure, it's bleak and rather harsh; but honestly, that's life. And I could easily see that's exactly how life might be in the wake of Nuclear Holocaust. A fun series to say "what if" to.
Halo - Originally, I was not a fan of this Pop Culture icon of a game. But as I played it more, I actually got over that and started to like it. Probably one of the few FPS's that I'm actually good at. The customizable armor and logos is what got me hooked, really.
Metal Gear Slid - Okay, everyone knows Snake owns. And when I played the first game, I had a lot of fun. Now what I really want is MGS3 and MGS4.
Super Smash Bros - I kick ass beyond measure in all these games. I can go toe to toe with the hardcore players because, hell, I am one. I know each and every secret in all the games, how to unlock every character and stage, as well as how to get every trophy in Melee and Brawl, so on and so forth. The series stands out because it's tossing all my favorite Nintendo Characters (and Sonic and Snake) into a ring and seeing which of them comes out on top.