Personally I am still uncertain as to how things will play out this fall but Larry Sabato (a fairly well respected and neutral analyst) is calling the House a done deal and the Senate as in play.
I do think this will be a bad year for the Democrats, off year elections almost always are for the party in the White House. I also think that for each party the worst outcome would be narrow control.
And of course we must factor in the Tea Party and its ability to screw everything up for the GOP.