Valkyrie

I'm going to describe this film with a phrase I read in another review - exceedingly competent. Everything is done satisfactorily, the film kept my interest for two hours (which isn't an insignificant accomplishment considering you know the ending going in - Spoiler Alert they don't kill Hitler), and nothing in it particularly annoyed me. The filmmakers picked an interesting story to follow, and in general it was fairly well cast (yes even Mr Scientology was fine). However I didn't leave the film with a particular desire to see it again so do with that what you will.
If you do see this film and want to see some other WWII assassination movies I recommend The Dirty Dozen: The next mission. This gets around the whole pesky constraint about not being able to actually have Hitler Killed, by having the protagonists kill some other much more threatening Nazi instead. However if you want to get some WWII entertainment that doesn't feel the need to be constrained by what actually happened than read Phillip Dick's The Man in The High Castle. The book takes place in an alternate reality where the Axis won the War, and all I will say is this is one of the few pieces of fiction that completely blew my mind. I walked around for a good ten minutes afterward trying to figure out what I'd just read. Seriously you have no idea what you're getting into. I don't know if this is a recommendation or not, but check it out. Especially if you enjoy Acid trips.