Having recently platinumed Killzone 3, it would be stupid to say I didn't enjoy the game. That said it wasn't everything I had expected it to be. Let's start with the basics for offline play:
Killzone 3 plays really well. Its style of shooter is different than Call of Duty and really sets itself up uniquely. The missions are still very linear, but they allow you a couple different ways of doing things. For example, there is one level where you are in a sort of trench and you can just run through it, clearing out the enemies within, or take the high ground and wreak havoc with a flamethrower. These different strategies in the levels are what really give you replay value.
The guns have been made less "bulky" than they were in Killzone 2, and I think this is a very good thing. Killzone 3 doesn't give you the speed that call of duty does, and that is fantastic, but it's also not so slow to the point of being a hassle (the second one in my opinion failed to do this).
The guns are as always quite diverse. The boltgun returns (a big favorite of mine) and you get a gun that looks like something straight out of District 9, just imploding the Higs. The problem I found with the guns though is that no matter what gun your using, your "heavy" weapon will always be best. Rarely did I even use my assault rifle weapon because the heavy weapons were so much better, and the game has so many ammo points that it is easy to just resupply and continue using it.
What can you say here? Flawless. Best graphics of any first person shooter out there. The cutscenes look great, the in game action looks great, and this transfers to online beautifully.
The sounds in the game are exactly how they should be. Whether your in an exoskeleton and the machine is beeping at you for low health or RPGs are blowing up in the background, it feels just about like your really in the action.
There are a few hiccups at times when playing co-op however.
There are four difficulties in Killzone 3: Recruit, Trooper, Veteran, and Elite. My first playthrough was on veteran difficulty and it felt pretty fair. All fire fights and true FPS action seemed about right, but when they tried to mix the game up, that's where the problems came in.
On a couple different missions, you are in vehicles, I won't spoil anything, but the difficulty when in these vehicles is downright unfair in many of the missions. Two in particular are unforgiving, the snow mission where you drive a futuristic snowmobile-tank hybrid, and the mission where you are in a space vehicle. I found myself dieing in these missions after no fault of my own... Frustratingly restarting at checkpoints only to have it happen again. Eventually you'll figure out how to do it just right, but it's a little tedious.
As I said before, I have gotten the Platinum trophy for the game. To do this, you must also beat the game on elite. My gripe is this, after having beat the game the first time on veteran, beating it on elite was actually easier and faster for me. The enemies took more shots and did more damage but it didn't seem like they were really any "smarter".
*Side note: on all difficulties that I played, the Higs can through grenades with 110% accuracy, forcing you out of cover.
Killzone 3's online still has a lot of work to be done which is sad. While day 1 patch 1.03 and newer patch 1.04 helped fix a lot of the bugs and connectivity problems, there is still a balance problem that I fear won't be addressed. Frankly there's just no point in not being invisible. You can kill people with the marksman's fully upgraded secondary weapon and still remain invisible. Fun to do, very annoying to be killed by.
The classes are diverse though, and if there were no marksman or sniping, it would be much more balanced and stress more team play. The Operations game mode is incredible and adds a lot more fun to traditional online play. The only problem is, it's found on only 3 maps and they have no plans on making more.
Another online drawback is the lack of squads. A great feature in Killzone 2 is now gone and frankly it makes playing with a friend a little less of a team experience. It's a pretty frustrating thing to have taken out.
The best part of the online though is how it is true to Killzone. They made the guns a little less "bulky" but that's about the only difference. It still plays how it feels it should and the graphics are amazing.
The clan system is also much improved from the valor point system. Unfortunately in order to get a good rank you basically just camp in one part of a map invisible and destroy the other team when they walk by. A simple fix that would stop this would be to make every clan have to have 1 of each type of class before they can have repeats. This would make matches much more competitive and fun. Unfortunately I doubt we'll see such a fix.
In the end of it all, Killzone 3 is a great experience. Campaign is fun and a good thing to come back to especially with co-op and online offers a lot more hours to play. I just hope custom rooms with no snipers start to pop up because frankly it's just unfair.