Havoc hand't even been born yet
Sebastian Shaw was never a Nazi, that experimented with/on Mutants, Mr. Sinister however, was.
Magneto getting his helm from Shaw was lame
Darwin's power doesn't make any sense. Adaptation means you adapt to your environment. So him growing gills made sense but him adapting to absorb a bullet? Nope, shouldn't have worked that way.
Angel the Pixie that shoots flaming hairballs was lame, so many much better characters to have chosen
Emma Frost is too young to have been there too
Beasts makeup after he mutated was LAAAAAAAME!!!!!!! >
Magneto did NOT help build Cerebro
Mystique was a little ho, falling first for Charles, next for Beast, and lastly for Magneto
All in all it was an enjoyable movie but like the OP stated, it was NOT made with fans of the comics in mind.