Well I saw it this afternoon and thought it was good. Certainly this wasn't a history lesson taught [to me] in school so it was nice to see it get some attention. The first half hour was a bit so-so but it quickly picked up from there, especially during the initial attempt that was aborted when they discovered Himmler wasn't present.
Cruise did a good job but I can't say his performance was drastically different than other films I've seen him in. The others gave fine performances as well, particularly when they were arguing about whether to go ahead with the mission even though they had no actual confirmation that Hitler was dead.
My favorite scene was probably when Stauffenberg has to get Hitler to sign the revised Valkyrie plans. There's a shot after Stauffenberg asks him to sign them where Hitler is a ways away in the room and slowly walks up to him. That was staged really well: By making his walk seem longer than it really is, it increases the tension.
"Ah, crusty pants, a filthy wall, good morning!"