I just bought this yesterday, and played for a good hour. I'm really enjoying it so far. My first experience with Killzone 1 was a few years back, playing it on my PS3. I really enjoyed it then.
The game design is pretty straight forward, but even then, you can see what Guerrilla Game's ambitions for the game were, despite the technology not being able to keep up at the time. I'm really enjoying the gameplay, now that it's much smoother, and no longer hampered by the PS2 hardware. I've been getting headshots pretty easily, although I had to tweak the control scheme to get one that I was comfortable with. Things like switching the Zoom button, and the Alt fire buttons, etc, stuff like that.
I've always loved the Killzone story and lore, but was really disappointed that the series never did enough with it. I've said it before, but I'd love to see the Killzone series get the Mass Effect treatment. That is to say, I'd love to see it go the RPG route, but keep the first person perspective. Set it during some of the earlier conflict, let us choose between playing as Helghan or ISA, and just really go deep into all that interesting backstory. I think the environments of Vekta and Helghan are fascinating, and would love to explore them more. KZ2 and 3 had this amazing detail and atmosphere, I just wanted to roam around. Give me an RPG, set on one or both of those planets, and I'll be in seventh heaven (maybe go a Fallout 3/New Vegas route, minus the crippling bugs. Lol).
I wouldn't mind an overhauled, maybe even scaled back graphical engine, to accommodate the larger scale. Although, personally, I'd prefer it to be a PS4 title. That way, it could keep the graphical fidelity the series is known for, but expand it.
I think the original Killzone is very underrated, and it was doing gritty realism before many other FPS series conned on. I'm enjoying the look and feel of this, and I miss not having the 4 playable characters in the sequels. Either way, I think KZ is a pretty solid series. 1-3 and Liberation were all pretty good. Is a lot of the resistance to the franchise due to the media hype and backlash of KZ1, and the CG target render of KZ2?
I'm glad I dropped the $15 on KZ1 (already own KZ2 and 3). I'll sink some more time into it later.