Mass Effect 2 is a big game, such as mos role-playing games are. One disc won’t settle it this time around; BioWare has two in store for the sequel.
Don’t worry, BioWare community manager Chris Priestly assures that it won’t be a nuisance switching discs as it’ll only happen once “at a carefully planned place in the game”.
“Even though there is a disc swap, it occurs at a carefully planned place in the game (that does not interfere with gameplay) and is done once,” Priestly wrote on the Mass Effect 2 forums. “You do not swap back and forth. 1 swap and then done.”
Sounds fine to me, Priestly.