Soma said it already, but Bob you don't need the DS to unlock characters. The DS just unlocks them faster than clearing story.
I've given this game an 8 or 8.3 - Your totally right the game is much more fun with friends, but my friend played me and I made the mistake of using Alucard first, he basically copied my play style which pissed me off, but in the end I realized that I could do other things with Alucard as well, next time I play him, I'm going to do these things to him while he does the simple stuff that I used to do.
The game has a depth to it, that I'm discovering, moves that are very particular, the move set may not be huge but MvC didn't have a huge variety either and that game was great. I know this game is very good because I've explored it, it doesn't get a 9 because of the online component, which isn't all too strong. But no where near as bad as Brawl.
By the way great games Soma, I'm going out in a bit.