So in this game you decapitate like a million orks and then shoot a bunch of chaos. That might seem a bit obvious but the distinction is actually important.
The first half of the game is about wading in, throwing grenades, sniping the rokkit launcher dudes, dodging nob attacks, stunning and executing enemies. In short, it's hectic, and somewhat hard. The game gives you a bunch of different weapons and lets you change them pretty often and it all adds up to an interesting experience. By the end of the third chapter you'll be drained but confident that you can beat all the orks, so the game changes it up.
The second half of the game is about hiding behind cover and shooting everyone from as far away as you can manage. Huh. Sounds like every FPS made in the last few years. This unfortunate change is because the Chaos marines use the same strategy as your own marine buddies do, i.e. dig in and shoot. There are also the Sorcerer units which laser beam you if you stay out in the open for too long, but they make a nice satisfying -pop- when you hit them with a charged Plasma shot, so they're okay. The melee dudes run at you and engage you in some pretty one-sided combat; if you don't have the Thunder Hammer, it's going to be pretty tedious to wear them down. If you
do have the Thunder Hammer, you only have your Plasma Pistol and Bolter to go on, and that makes fighting the Chaos horde a lot harder. I guess this section is meant to make you choose between raw melee power and actually-being-able-to-shoot-people-worth-a-damn but the choice is hollow because the Plasma Rifle is too good.
The finale is pretty badass and befitting the whole game, and the ending cutscene made me smile because I basically knew it was coming, but it fits the W40K world very well.
All in all I did enjoy this game. It's a lot of fun and it is definitely intense. I like this take on the W40K game but I'm still, STILL waiting for an honest recreation of the board game in video game format. Not that I expected this to be it; Space Marine excels at what it set out to do, namely: let you tear off Ork faces.