The music by Chris Yong sounds Elmman-ish enough for me that it does not brake continuity.
But lets face it you know Elfman would have done a better job!
There was a rumor circulating around the 'Net that people who have seen Spider-Man 3 said that there was only 10 minutes of original score by Christopher Young in the film and that the rest was temped tracks.
Dan Goldwasser, who has seen the film and attended the scoring sessions (he runs Soundtrack.Net) denies it. He says that Elfman's main title theme was re-recorded with Young's themes sandwiched in, but most of the film Young scored using Elfman's themes. Goldwasser did acknowledge there was some temping in the film, but not to the extent that Spider-Man 2 was afflicted with.
In the end titles, the music accreditation is like this:
Danny Elfman (themes)
Christopher Young (score)
John Debney (additional music)
Deborah Lurie (additional music)
Steve Bartek is credited as an orchestrator, so he orchestrated Elfman's themes into Young's score and helped maintain the sound of the first two movies' scores.