I just finished this and was really disappointed. Compared to the second one it seemed short, rushed, hollow and linear. The best part of the second, for example, was playing through all your team mates' backstories, of which there was a good amount and the characters were varied and interesting. The team mates in this one were really dull and I didn't bother to talk to any of them much.
On top of that it was all a bit too macho "this is it", "show them no mercy", "raar, we are soldiers" nonsense. The graphics seemed really uneven, with loads of low resolution textures knocking about. It seemed like the new models and textures were shit and the ones they could use from the other two games were nice.
The ending was OK. By that point I was kind of just doing as I was told anyway.
Oh, and the combat is boring. And turning it to "story" mode makes it even more boring.