I've only played RE Remake HD, RE4, RE5 and I believe Code Veronica (one for Wii, on rails).
Revelations 2 is my favorite already. Hopefully it will maintain its quality in the next episodes!
RE4 has a damn great atmosphere, much better then RE5 in that regard. However the co-op addition in RE5 still pleased me more. Revelations 2 brings a better atmosphere then RE5 (IMO), better gameplay, interesting co-op mechanics and that amazing Raid mode.
Its a sin not to buy Episode 1 for 5 dollars! Everyone that likes shooters, or zombie games, or survival horror games or Resident Evil games should try it! Its a bunch of content with a very high replay value for its price.