I basically mirror most of what you said. The first half of the film is the best part, once the inevitable villain enters I lost interest.
Emma Stone was under-utilized, she's better than average but wasn't given nearly enough to do. The romantic aspect is actually the part that interested me the most, too bad it lost screen time to the overblown CGI.
The film felt rushed, too many aspects were quickly mentioned and then discarded to keep it rocketing along at a fast pace, but I think they lost a great deal of the detail necessary to make it work. Raimi's Spiderman works because it took the necessary time needed to tell the story effectively.