Indeed, the ending does have weight with Eric being responsible for Xavier becoming crippled, I really liked that. But that's something that could just as easily have happened in the second or third film after more time as them being friends was being built.
To look at this from a Star Wars prequels sort of way, little is shown in this of movie about Magneto being "good." We're shown pretty much from the beginning he's got a dark side that lurks in him so there's no surprise when it turns at the end, this his turn isn't tragic but it's expected. Much like how Anakin Skywalker was treated in the prequels, he's a douchebag ranting about wanting power and being controlled the whole time, his flip isn't a surprise because he was always presented as being on the precipice anyway.
We should have seen Xavier truly turn Erik away from his revenge desires, made him want to do "good" for mutants and then in some future movie some need for revenge pushing him completely off the edge. He should have spared Kevin Bacon's life and let him get captured/reprogrammed by Xavier/the military, claimed himself the "better man" than gone out do fight with the X-Men to stop the military. Then in a future movie he reaches a breaking point when the lengths humanity goes to in order to stop mutants finally pushes him too far and Xavier's optimism is no longer tolerable and he feels swifter action is called for and we see him, as a middle-aged man, beginning to work on his plans for the mutating device he has in the first X-Men movie.