I've found it really needs to be played in co-op on the campaign, else it can get a little repetitive on your own. The mission types are the same all over the map - i.e. hostage rescue, clear base, plant bug, recon area etc. If you've got a couple of mates who have it or willing to try it, it can be a good laugh though, especially trying to co-ordinate missions where you need to do it undetected, and one of your mates happens to be a wannabe Rambo.
I haven't tried the new PvP multiplayer mode yet, so can't really comment how good that is.
It looks great, and the gun-play is quite good, there are hundreds of different weapons to collect and numerous modifications for each. Fairly low key RPG elements with the skill system/resources etc so there is at least a sense of progression.
I believe there's a 5 hour trial or something like that you can download. That'll give you plenty of time to see most of the mission types and form an idea of whether you'll like it.