I thought the enthusiasm for Obama would be down a lot this time around and it was because people know who he is now. I think the biggest reason the Repubs lost is that people just did not get very fired up by R&R either. I think it probably did not help that the GOP picked the only candidate available who could not attack Obamacare with any credibility.
Secondly, as time went on and some of these characters dropped out of the race, Mitt Romney actually got less popular among primary voters. As the primaries went on through January, February and March, he piled up delegates even as his share of the "popular vote" in those primaries declined. When a guy wins a primary with 35% support, this tells me that his own base wants someone else.
My one suggestion at this point for Republicans moving forward is to get rid of the garbage in the primary season and consolidate the race to two candidates -- a "Tea Party" candidate against an "Establishment" candidate.