KILLZONE. Honestly, I played KZ3 recently, and just from the starting cinematic it was like "now that the combat is over for a little while, the Helghast are getting organised again, so we sent in a bunch of colourful characters to wreck that s***". I've never seen a real reason to try and murder them all, they should have been allowed to declare independance and everyone just leave it at that. Aside from that, the Helghast have interesting technology, used to be the underdogs in a big way, and all look like little Darth Vaders. What's not to like?
P.S. In the God of War series, I can't sympathise with Kratos at all. Killing Ares and a few of the other gods too I got, but he just murders everyone in his way (especially what he did to Midas). This makes him a badass, yes, but it also makes him a prick. There are plenty of badasses that don't feel the need to murder innocent people and still have the same awesome. Kratos is pretty much a plot device now; any bullshit he's had to endure at the hands of the gods is paid back in blood, now he's just a reason for gods and titans and whatnot to be killed.