
Read countless of posts from hardcore raiders calling BWL and AQT suitable for blue/green players and that Naxxramas would be the "real deal".
Imo, I'd say that up to Chromaggus and up to Twin Emperors can be done with blue/green, sure.
Up to is not including of course.
Excluding some nasty stuff like Onyxian Scale Cloaks and NR equipment of course.