Well, that's the reason it's called Playstation All-Stars instead of Super Sony Wars or whatever.
The advertisement was bad, yeah, but it really only impacted a couple things, all the pointless DmC content, Raiden's inclusion (though I liked Raiden), but it still brought in a lot of characters that nobody had really heard of before, like Emmet Graves or Sir Daniel.
Really I wouldn't have had a problem with it were it not for the lack of some of the most iconic Playstation all-stars liek Crash or Spyro or Lara Croft.
I liked the supers only thing, it put an interesting spin on the platform fighter genre, aka only Smash Bros. because if anyone else dares to touch that suddenly they're ripping Nintendo off and are a sellout.
I couldn't tell you how much it actually enhanced the gameplay, really that kind of thing is probably what led to the game being so predictable, and contributed heavily to how overplayed Raiden was, but I like that they did something different.
And the stage mashup concept is the greatest idea ever and you'll never convince me otherwise.