This is my first time playing a red faction game and I must say that it is pretty fun just blowing everything up and causing mayhem.
The missions are varied and interesting but some of the side missions can become tedious (saving prisoners). But the good thing is that you don't have to do those, there are plenty of other side missions to get the job done like riding along with an NPC and blowing up as much stuff as you can in a specified time - awesome! And if that doesn't sound fun, you can also choose to go around and blow up EDF buildings to reduce their influence and skip the side missions altogether; excellent execution of sandbox game design.
Unfortunately, the driving is pretty bad and the steering on most vehicles feels unresponsive. And you will be doing quite a bit of driving across the vast world (no load times though) so get used to it. Also, the weapons weren't very satisfying. I used every gun in the game, but stuck to pretty much the same loadout I started with the entire single player campaign. The lightning gun kinda sucks and the grinder isn't worth wasting one of your valuable 3 weapon slots. So, you have to keep the remote mines for when you need to blow buildings, a gun (i used the rifle) for the enemy troops, which leaves just 1 wildcard slot. I used the rocket launcher until I got the nano forge. In general, I think they really dropped the ball and could have provided some crazy cool weapons but didn't.
Just make sure you play it through to the end, because the last couple hours of gameplay are by far the best part of the game.
I cannot speak of the multiplayer because I did not try it.