Was Magneto's character interesting? Yes.
(Just like in the comic book) Magneto isn't supposed to be evil and feared. That's what makes the character and conflict interesting - you can actually understand his viewpoint. Considering his (retroactively added) history, he sees Mutant registration as just the first step in the slipperly slope leading to the of branding mutants and herding them into concentration camps.
Was the threat perceived by Magneto actually a threat? Yes.
Congress may be ineffectual, but all it takes is one bill to start broad socioeconomic change and head down the slippery slope just mentioned. (e.g. - prohibition) To me, this means the plot is completely valid, and the conflict very believable. Think registering those who are feared is ridiculous? It happened to the Jews, was discussed with AIDS, and happens with sex offenders.
Was the plot silly? No.
Magneto wasn't trying to promote peace and understanding. And he wasn't trying to take over the world. He wanted to prevent the Mutant Registration Act from passing. Period. Not only here, but in other countries, as well. So, how did he go about doing this? Well, he figured, "If the leaders of each country are mutants, they will be a lot less likely to pass a law that discriminates and persecutes them." Maybe its a reach, but there is at least a line of reasoning behind it.
Fourth - Not all long time fans are "rabid." I've been reading the comic book for over 20 years. I don't mind minor changes to the X-universe, as long as it makes for a good movie. I don't mind if they to do away with spandex (contrary to what the idiot reviewer at EW thought). I don't mind altered histories. I don't mind Wolverine being too tall. He had claws and looks close enough to recognize. Good enough for me! All I wanted was a movie that wouldn't make me embarrassed to be an X-fan. I got that and more. I got a GOOD movie. It was a good action flick. It made me laugh a few times. It had some SFX that made me go "Wow!" That's all I expect from ANY movie. X-Men is a movie I can happily recommend to my friends. And hopefully they will walk out and go, "Wow. That was cool. So that's why you've been into the book for so long..."
And if nothing else, I now know how to prove I'm not a shapeshifting imposter to my friends...
"Time is money and money can't buy you love and I love your outfit" - T.H.U.N.D.E.R. #1