Days Of Ruin's Campaign is harder than the normal campaign for AWDS, but it lacks a hard campaign after that.
There are trial maps that are unlocked as you go through the chapters, and other trials map after clearing the initial trial maps. There is also a free-battle option to play other pre-designed maps, and you can also connect to wi-fi to play others as well as download player-created maps and the ability to upload your own (limited to one, though :/)
I enjoyed the animation for DoR, and the difficulty seems to be a roller-coaster until you start getting near the end, then it begins to build up. The last mission was ridiculous, but according to my bro, nothing tops Crystal Calamity on Hard in Dual Strike.
I would recommend the game, I've already logged in about 60 hours and still have a couple trial maps to complete, wi-fi is decent but people continually disconnect on you if you have the upper hand, and especially if you're going to deliver the final blow.