Looks good. The art shines, the scale is great, and the technical wizardry is impressive for a launch game. Not much in face value that hasn't been done by some high end PC games already (Crysis 3, Metro: Last Light), but that's a compliment. Glad to see some snazzy effects finally adopted by games, and by a series well renowned for presentation no less.
My feelings towards the Killzone series as a whole are pretty damn scattered, but I will say that the most impressive thing about Shadow Fall to me is what appears to be more open level design. I wasn't fond of the painfully linear campaigns of Killzone 2 and 3 and felt neither did that particular formula very well anyway, but Mercenary, even if it didn't live up to what I hoped, showed that the universe works better when they loosen up the pacing and level structure to let you think a bit instead of monotonous cover-to-cover shootbang.
I get a Crysis series vibe from Shadow Fall, and in a good way. Could be what the series needs.