Romney had his issues, but I think he was a pretty strong candidate and could have won in other years. People underestimate the strong connection Obama has with his base.. for all the people who hate him, his approval rating has had a floor not like those of other Presidents.
I would argue that the strength of his bond with a certain segment of the population is stronger and wider than many modern Presidents.. I'd compare it with any actually. The country went through some very difficult things under his watch--the recession, ending the Iraq war which had really inflamed a lot of passions, killing Osama which again just healed an old wound for a lot of folks.
I'm not saying you have to love the guy.. I think you have to recognize that other people do, and for a combination of reasons that is justifiable with someone of a given experience (let's call you the anti-war mother of an injured iraq war vet who was about to lose his job at GM and also can't get health insurance because of pre-existing conditions.. you'll probably LOVE Obama, for reasons having nothing to do with him 'giving you stuff')
I'm also not saying he has been the most popular President. I just think his base has been larger and more durable.
Combine that with his extremely well run campaign and he was unbeatable. His main campaign team were 3 of the most talented politicians in the country (Obama, Clinton, and you're a fool if you don't think Biden can work a crowd). His campaign staff have been called the greatest ever and highly innovative (Messina, Plouffe, Axelrod)