One of my favorite Final Fantasy characters is Tidus. One of his main traits is that he knows how to loosen the tension by laughing. He's a cheerful person.

Yeah, ripping someone's tongue out is as relaxing as it can get :)

Baird in Gears of War has a pretty dark humor. But it is way more funny to see him totally ignored by the rest of the crew; like when he fixes the tank in Gears of War 2, and he says "Fixed it!". Nobody replies, he goes to "Thank you, Baird!". He ended up saying "No problem, fuck you guys".

Jak & Daxter

You can catch some of the humor just by looking at the trailer

haha, i was talking of Lego City Undercover

lol

How on earth has no one brought up the Paper Mario series?!?!?! I've laughed harder playing that game than most comedies I watch.

Drake and Sully banter in Uncharted, the small jokes in Metal Gear Solid games, the radio stations in Grand Theft Auto and the humour was just non-stop in Persona 4. I think video games have enough humour, and it can be out of place in some games anyway.

Oh, and that reminds me, I still need to play Portal 2!

Monkey Island games certainly set the standards. The Portal series is perhaps the most humorous in recent memory.

Another series I found to be quite hilarious, and unmentioned as of yet, is the Disgaea series.