I played this game through on the 360 and it's pretty awesome.
Unlike previous RF games, you can't harm the ground in this one. However, EVERY structure in the game is destructible. The destruction feels really substantial and looks and acts great. It's far better than I thought it would be, and I didn't miss not being able to blow chunks in the ground (though I thought I would). The game generally remembers everything that you've destroyed forever (sometimes the game pretends like you never leveled a particular structure if it needs to be present for a mission). Very cool.
I get bored of most open world games, and I could feel the repetitiveness trying to creep in on this one as usual, but Volition did a pretty good job keeping it at bay and I actually managed to beat the game (only other time I did that was with Assassins Creed and there were mitigating circumstances that time). The main story missions are fairly original most of the time with the final missions providing a very solid ending. The optional missions in each area are relatively diverse. The reason to do them is to lower EDF control and raise sector morale. There are other ways to achieve these ends besides the side missions, so you can mostly avoid side missions you don't like. Sometimes a dynamic side mission will become available where the EDF is suddenly attacking one of your bases or a convoy starts traveling through a sector out of nowhere. You can ignore them with no ill effects, but it mixes things up a bit from just having all side missions being static blips on a map waiting for you to get around to them.
Ultimately the core gameplay revolves around shooting, blowing stuff up and driving. There are a few odd construction robots lying around that are pretty awesome and a bit different however.
What really sells the core gameplay is the detail and utility of the destructible buildings. These are really substantial looking structures that you can go inside of and such. They were designed meticulously with a supporting frame covered in decorative materials. Come to think of it the only odd thing about the buildings is that none of them have doors
I really didn't notice the whole time I was playing. Anyway, you can drive a vehicle through a building (provided the speed and weight of your vehicle match up well with the strength of the building materials) to bust it open and rescue prisoners. You can plant charges on the back of a vehicle and use it as a mobile bomb (after you've left the vehicle preferably). You can drive a giant earth mover, but unlike most vehicles if you drive it off a small cliff it's going to lose a huge chunk of it's health bar.
All in all they just did a lot of things right in this game. It's a lot of fun to play, and this coming from someone that usually falls asleep playing open world games (haven't played more than 30 minutes of GTAIV or 3 hours of inFamous).