From someone who's never played any of the DOA games before, I'm absolutely loving DOA4. It's an absolute riot, solo, 2P or online. I'm a little frustrated with the gameplay now and again (seems impossible to block or reverse at times), but it looks great and it's tons of fun.
As I get better I'm getting in to the nuances of fighting with my fave characters, so it seems there's some depth, too. Haven't touched any of my other 360 games since I got this