Serious Sam 3
It's - eh. It's ugly and all the new enemies suck. The helicopters are extremely difficult to hit unless they hover in place (our you use the grenade laucher, since its projectiles fly faster than the rockets) and since you're looking up do kill them you're open to all manner of things sneaking up on you. The tentacled women that go invisible and squish you with telekinesis are just tedious to fight, since you have to wait for them to uncloak before you can hurt them, even if you spot the shimmering of their camouflage. The hell monkeys are only midly irritating in comparison and easy to fight (or even ignore), which makes them a weak addition. The new melee moves break the spiders, both big and small. Unless they're coming from all sides you can just melee them all.
Maybe I'm remembering the first one more fondly, but the level design wasn't always this weak, was it? It gets boring especially towards the end, with gigantic arena after gigantic arena and straight tube levels that get longer and longer. Doesn't help that a particular sequence (collect four orbs, activate ancient alien tech, fight warship) repeats.
Cardinal sin: Introducing new mechanics during the final boss fight. Oh there's a jet pack hidden somewhere in the boss arena that I need? Fancy that. I stumbled upon it only by chance. Oh there are piles of metal pipes that I need to stick in its back to stop it from regenerating? I would have never thought to do that, but thanks.
Meanwhile you're getting shot at from all sides with the gigantic boss both shooting at you and trying to trample you. What a fun learning environment.