As great as Rocket Raccoon is, marketing for this film I think will benefit tremendously by focusing on the "band of misfits" cast diversity and sheer lunacy of the spectacles. Showing strong, likeable characters with interesting, snappy banter between then has a better chance of luring in new fans as they quickly grow attached to particular groups of characters and want to see how they develop.
It's not an impossible thing to market a blockbuster/superhero movie without having the groundwork done by pop culture. If it were, we'd have no original premises ever. They just need to remember marketing it as something familiar, like The Avenges, isn't going to work. It's gotta be marketed as a fun new adventure, not a culmination of familiar faces.
EDIT: I also think it's impossible to judge how this will be received until Marvel actually bother pushing it in the mass market streams.