These are my initials impressions, (I will amend this review as I play):
Right off the bat, this is the stupidest game I've ever played, and kind of racist. Having said that, I am enjoying it so far. The graphics hold up well, perhaps a benefit of the crisp and vibrant art style. The environments are very colorful and imaginative and a joy to explore (even though the game is not particularly open-but more on that later). Though a Serious Sam title, this particular installment shares little with its predecessors- it's brighter, less serious and seemingly
more kid-friendly (older siblings and parents take note, this game still contains excessive violence and "adult" subject matter, but on the whole seems more like a "T-rated" game than an M). Also, the gameplay is more akin to the recent Shadow Warrior reboot than the original Sam titles (which is a good thing in my opinion)-the levels are big and spacious but at the same time very linear; progression is from one area to the next, broken up by cutscenes. The shooting is fast and fluid, as you'd expect from a Serious Sam game, and generally pretty fun. Oh, and you can ride dinosaurs (I would have tried this but I killed mine accidently). But by far the most striking aspect of the game is its tone, and if you come into this as a veteran from the originals, prepare for a shock. This is not necessarily a bad thing, though, and from the little I've played of this game so far, I can tell it fills a unique niche that the others do not-namely, a creepy early 2000s CGI young adults' action adventure/scifi movie/ Conker's Bad Fur Day-type "adult masquerading as kid-friendly" niche (I guess that sort of thing was popular in the early 2000s). So anyways, those are my early insights, but I'll have to play more and perhaps I'll have more to say. Despite the frankly idiotic story, I recommend this game, for now.
Update: I played a little more and the charm of the game really took hold. The story is even beginning to grow on me (Sam's horrific one liners are not, however). Honestly, I'm surprised that Serious Sam 2 manages to look and play as well as it does on modern hardware, so that's a good thing. I prescribe this an an antidote for Call of Duty.