Okay, I've nearly finished it.
I don't know if I'd buy this game, it depends how much you can afford it and your tolerance level for games.... I'd say this game is a perfect rental game, fun to play, not very long and perfect for whenever you're in the mood for a Cap game, but as a purchase, I think it's more likely to gather dust in the long run than be something work owning, but again, that depends on your personal tastes.
As far as costumes go, I unlocked the Ultimates WWII costume like halfway through the game, although god knows how I did that, it didn't really tell me, and you can unlock the classic costume at some point. In the instruction booklet, they also say keep an eye out for Marketplace content to be released soon.
I'd say my two biggest problems are the graphics (all cutscenes are in game and look awful. There's no hint of that great prologue trailer CGI we saw, it's all SEGA's awful graphic engine, bad movement, awful lip syncing etc), with textures and explosions, which there are a lot of, looking very, very flat. A few environments look pretty nice though, like Zemo's Estate, so it's a shame that they couldn't go all out. Also, there is evidence of corner cutting in quite a few places.
The other thing is the controls. The fighting is great, but movement is pretty horrendous two. The only speeds are pretty much stiffly running or snails pace, and I found myself running into walls or missing stair case entrances several times because of the imprecise movement. Also, there is total inconsitency with how you interact with the environment. If you're high up, you can usually jump down, however if there's a waist high fence or railing in your way, instead of just leaping over it, you do a physically impossible wall jump of an invisible wall above the railing. This became more annoying when, after 4 hours of being unable to mantle things like that, the game let me do it in one section, then never again. Little things like this, for me, just totally took me out of the game in feeling like I was Cap. When you're fighting a room full of guys, it's awesome, you're head snapping, leaping over guys, shield throwing, everything you should be, but then most fight scenes end in about 30 seconds to a minute and then you are back, climbing a ladder extremely slowly and very uncaplike.
So like I said, it's been fun for a Cap game but I don't want to sell this game as awesome, when it has several clear flaws.