I really hope we get to see more of Walter with all of his brain as the show progresses, either through flashbacks or alternate dimensions or whatnot. That small taste we got in the most recent episode surely can't be all we're gonna get.
And I hate to say it - but the more I watch, the more I'm convinced that Walter might end up being the bad guy. What, exactly, "being the bad guy" means, I'm not too sure yet. But it's obvious that when he had all of his mental faculties about him, he was a shrewd, calculating genius. No telling what he was up to before they chopped his brain up.