Armored Core series. Because Piloting 2-digits tons of steel up to the speed of sun while being more armed than a tank batallion is just "fugg'n awsum"! The designs are great, the versatility is huuuuuge and has some crazy thought out concepts - though that also makes it a little stat heavy while constructing your death robot of annihilation.
I like "For Answer" the most in the series because of it's sheer ridicolous speed, imo that version captured bad-ass mech fights the best - fuck realism
Then of course the Saints Row Series starting at #2. I like each of the games for what it is and 3+4 are easily part of the most wacky, zany and over the top games i've ever played. But it's done well. It didn't only adapt to madness it embraced it, rolled around it and probably had some sweaty love with it too.
And newer to the list: Darksouls Series. Because after beating that game you feal badass. Aaaaand i noticed that it's from the same guys who did Armored Core (*cough* roughly 20 hours into the game while seeing their logo a bajillion times *cough*) that explained alot of the mechanics and the loads of diffrent stats there are
Currently playing the 2nd iteration and it's neatly handing me my ass on a silver plate. Personally i feel the newer game is even harder but that's maybe also linked to the fact that im currently playing with KB+M and not with a controller since the game has an issue with mine - KB+M is alot better than controllers in some aspects of the game, mainly while not locked on but due to the limited button mapping i'm currently unable to perform reliable parries and not able to do jump attacks at all, but maybe i can figure out a mappin' that makes sense for those too.
There are some more, but i won't explain each and everyone just a quick rundown:
Civ Series 1-5 (no 4, but count Alpha Centauri instead)
Monkey Island. No cut that. All the classic Lucas Arts Adventure games. They were probably my first games i've ever played +20 years ago. MI, Zakk, Loom, Indy, The Dig (a lil later) and the Maniac Mansion.
Diablo 1+2. 3 can die in a fire.
DotA, Binding of Isaac and Mass Effect.
PS: Also im a crazy Freelancer fanatic, but i tend to avoid to talk about it because then i remember this game is already ~10 years old, there was never another game like it (Dark Star One was shite) and OMGSTARCITIZENWILLPROBABLYBEAWSUMIHOPEITDOESNTFAIL*gasp* Also Freelancer has a special place in my heart since it's the birthplace of my nickname and i haven't changed it since and used it in every online/Mp game there after.