The only real problem for me was the way Welles interrupted the brisk, years-are-flying-by pace of the film with that gruelingly long and sometimes tedious opera storyline. Don't get me wrong, it's a great anecdote that tells us a lot about the character. Kane building an opera house for the untalented singer he left his wife over largely to silence the critics who put her profession in quotes during his election bid, and then writing the scathing review of her performance himself. It's good stuff, but it could have been told in fifteen minutes, rather than forty-five.
Still, it's a great film, and you can use that conveniently large chunk of time in the middle to check your laundry or walk the dog.