As far as those expectations were concerned, it was disappointing. Though it might be less about subject matter differences and more about poor casting choices. Any time you try to use white folks to play Indians-- much less, try to write Indian-sounding dialogue for them-- you are damning your film not only to be significantly watered down by inauthenticity, but also subject to harsher historical criticism because of it. This alone made it extremely difficult to get into the film. There is no doubt that the blue-eyed Lancaster is a fine actor, but he is no Native American, and try as I might I could not see him as one. Jean Peters as the squaw comes off even less Indian than Lancaster. It is a compelling story, nonetheless (except for the ending, but I'll get to that); and while I'm not much for remakes, I'd love to see the film remade using actual Native Americans for the leads. I think it could be really powerful and thought-provoking.
As far as the plot goes, it's pretty consistently good until the love story gets in the way. I find it tough to believe that a hardened warrior like Massai would soften as quickly as he did, and even harder to believe he could be so easily domesticated-- at least the way it was portrayed. There also seems to be some kind of message in this (intentional or otherwise)-- that the Indians' best option was to settle down and grow crops like the whites. It worked pretty well for the Cherokees, right? And the ending, well, ugh. I was sure Massai was going to go down in a blaze of glory (apparently Aldrich filmed a different ending which I'm willing to bet was some variation of that theme, but was asked to shoot a friendlier version which was ultimately used for the theatrical release, much to his disappointment). However, even if Massai were to survive, there's no way you can get me to believe that the cavalry would just let him walk out of the cornfield like that without mowing him down right away.
I have yet to see more of Webb's writing and Aldrich's directing (I haven't seen Dirty Dozen yet, but it's high on my list), so I'm not giving up the hope that I'll see more great Vera Cruz-like dialogue; until then, I consider it a shame that Webb and Aldrich didn't work together more, or at least produce more great films like Vera Cruz.