Well, I completed the game last weekend. It's good, but I think I agree with many others in that the game does have various parts that are a bit of a drag. I only completed it on the normal difficulty too, but despite that, it didn't really offer much of a challenge, until the very last two chapters when you encounter enemies that are either unbeatable (bots) or just very powerful ones (or in enough quantity to make you think through how you would approach it).
On the whole though, the game was easy and being a bit of a bullet sponge yourself, it really didn't make me have to think much on how to approach the level. There were various instances though where I felt a bit lost - like where to go, but pressing the up-button to get the objective marker helped. Though by the amount I had to actually get the objective marker on the screen, at one point I was thinking it might have been a bit better to just always have it present.
As a game, I also think that it's not as good as KZ3. Truthfully, I kind of forget lots of stuff about the KZ3 campaign, but when I completed it - it was quite something. Lots of block-buster moments and a lot better than the KZ2 campaign. The only thing that was a bit of a letdown in KZ3, was the missing end-boss. KZ2 will go down as being very memorable because of that. Unfortunately, IMO, KZSF falls short in most of these areas. I liked that there was less large scale battles and that for the most part, you are more or less an infiltration / sabotage mission, but somehow, it still felt a lot less exciting than KZ3s. At some point, I was also quite bored too.
On the up side though, the visuals are amazing. Throughout the game, the framerate is suprisingly very stable (I rarely noticed any drops) and the graphics are just very clean and polished. On the down side however, you have the awful lip-synch and the very stale faces. Also, and this is perhaps just an inherent problem with how Guerrilla creates its graphics with lots of postprocessing, but I definately don't like the lag in the controls. It just feels as if you're playing on a TV with high latency display lag (100+ms). I get the weight argument, but IMO "simulating weight" has nothing to do with screen latency.
As for the multiplayer - I really haven't played much of it. Not sure if I like it - it definately feels better than KZ3 for what it's worth, but I don't like the verticality in some of the levels. I guess I just really miss the KZ2 maps - Tharsis, Radec, Salomon market - heck pretty much all of them were awesome and easy to play. In KZ3, I still feel lost, but I perhaps it'll get better when I start to invest a bit more time into it. Being a regular BF4 (and CoD versed player) though, it is a bit annoying that the other games make it so easy to just jump in and play (and have fun) while in KZ:SF, it seems like there's an initial learning curve you have to get passed first to see what would make the multiplayer so unique and good.