I'd rate it about a 9/10, 10 if it used it's own original engine; but the game itself is quite different. Basically, DoD, is comparable to a fast-paced arcade style of gameplay, while RO is more of a sim. After playing RO for a while, then going back to DoD, it'll seem as if you were playing Quake or something.
Also, I have 2 invites for the game, so if you want to try it out, I can send one over to you.