The...majority of games? Dunno, from my observations the majority isn't the super srs bsnss stuff. There are lots of big titles but a majority, no.
Anyway, and I cannot say this enough times, Magicka. Mega fun, and mega awesome. It somehow managed to conform to my ideals of a dream game AND I HADN'T LAID THEM DOWN YET! It has the most awesome casting system I've seen so far - something I've wanted for a lo-o-ong time, to make you feel like you're playing a mage with the command over the forces of the world. Also, it's choke full of humour and it's even funnier if played with a friend or more.
The Showdown Effect looks like a couple of barrels of fun, too. No wander, it's made by the same people behind Magicka.
No Time To Explain...well, I have the time, I just cannot. Watch a couple of minutes of TotalBiscuit's video [https://www.youtube.com/watch?v=vXi5tA4VVm0] to get the idea. It's about time travel...and stuff. And I think it manages to capture "fun".
Other than that...hmm, Game Dev Tycoon has been occupying me lately. Not "fun" as in "lighthearted"...not mainly, at least, but fun as certainly "entertaining" and "amusing". Quite addictive, too.
I've also discovered Minecraft. So sue me, I bought it, like, a month ago. That has its moments. If you're into it.
FTL: Faster Than Light is so awesome it needs a mention. If you like roguelike...erm, -likes. With spaceships.
Hotline Miami is, and I'll quote the threat title where I first heard of the game, "a bundle of joy". I cannot agree more.
Torchlight 2 is here, too. It's not "serious", it's not really "fun" either, not per se, at least. It is, however, a superbly good experience. Well, perhaps - your mileage may vary. If you've played Diablo 2, give TL2's demo a spin and see if you like it. Or, heck, just give it a spin - it's a really nice ARPG. Path of Exile is it's more moody and serious cousin, though - if for some reason you've played D2 and TL2 is missing something, PoE would provide almost guaranteed.
It wasn't too hard to pull off some examples of games that apparently are not the majority. I struggle to think of srs games, to be honest.
Oh...by the way, speaking of fun games, you can just go and get the Humble Double Fine Bundle [https://www.humblebundle.com/]. You're welcome.