Saw it yesterday afternoon. Overall I was pleased with the movie, though I did think the last little bit of the movie wasn't the strongest. Up until then though the movie was certainly very enjoyable and although the action was pretty ridiculous at times (Mutt fighting on the vehicles in the amazon, anyone?) that's kinda just the standard of action movies these days. Not the best but certainly an enjoyable movie. Personally I hated the new Star Wars movies and was scared when they were going to make a new Indiana Jones movie (a series I preffered) but my fears were for naught. It didn't hurt my opinion of the series at all.
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I'll admit at first, the presence of aliens actually did bother me but after some thought, it wasn't that big of a deal. If there could be the ark in Raiders, magic in Temple and the Holy Grail in Lost Crusade, why not aliens?