Actually, that's a lie. I do that all the time. If I didn't I'd go catatonic trying to decide what movie to watch. Let me start this thing over.
It's rare that I'll passionately dislike a film before even having seen it, but I've decided that this is the case for 10,000 B.C. after having only seen the previews. It's not that the film obviously relies on action, setting and spectacle to make up for a cliché plot; I tend to only muster up indifference for that sort of thing usually. It's just too common to deserve true ire. What's really pissing me off is just how badly they screwed up the history in this movie.
This criticism may sound strange coming from a guy who's cool with science fiction and has fond memories of the Lord of the Rings. After all, both the science fiction and fantasy genres have very little connection to reality, but it's that complete rejection of reality that makes the suspension of disbelief easy. I can accept magic, hobbits, oddly humanoid aliens, and the Force in the realm of fiction simply because they're far enough away from reality that its personification isn't sitting in the next seat throwing 'bows into my already bruised ribs each time something in the story wouldn't jive in the real world. 10,000 B.C. just doesn't depart far enough from the plausible to return to fictional plausibility. It's just a mash-up of two distant eras in human history. It's believable that the giant, flightless, carnivorous birds and mammoths lived alongside humans. Mammoths and terror birds overlapped in their times on earth and Mammoths and humans most definitely co-existed (although terror birds are thought to have gone extinct long before humans became humans.) I could buy that terror birds were a rare, but still extant hunter that late in the game and we just haven't discovered the evidence, but it'd be pushing it.
Mammoths and large, urban civilizations with a ruling class supported by the excess production from agricultural technology most certainly did not co-exist at 10,000 B.C., however. Hunter-gatherers gave up their wandering and took on the steady, but malnourishing, lifestyle of agriculture later. The first known examples of agriculture come in the 9,000's and urban civilizations aren't known until thousands of years later (basically around the Bible-based theory of the origin of the world around 6,000 years ago). I've been thinking this since first seeing the first ad a few months ago, but refrained from discussing it much just because of the fact that it made me feel like a dork. After reading an article that backed me up like a wingman during a night of clubbing, I couldn't hold this complaint back, though.
Despite my crippling criticism, there would have been a way to save this movie and return its plausibility for me. If it had turned out that this was all a giant alien zoo where the time-traveling curators collected examples of each of the phases of human history and the main character was simply an escapee from his enclosure of the zoo, I think, then, at least I could at least feign indifference.