This is one of the coolest, most interesting, and unique films that I've seen in quite some time, possibly (maybe) ever. To simply, this is a feature length version of the "Dawn of Man" segment from 2001: A Space Odyssey. It takes places (likely) in what is now Europe, only 80,000 years in the past.
The main story follows a trio of neanderthal tribesman tasked with going on a journey to find fire and bring it back to their tribe after the fire that they had been using and protecting tragically gets extinguished. This would all be simpler if they were more advanced and could make the fire themselves, but at least they're more developed than one of the other tribes depicted in the film.
The story is quite simple, but there's so much more to it than that. Besides being a basic man versus nature survival story, it's also very human and deep, and traces the development of man into a less primitive state of being. Four tribes are depicted in the film, all of them in various stages of development, and each with their own set of values, culture, and language or communication abilities.
The story starts out as interesting, and only gets even more so from there as the trio's journey takes them to places that alter their world forever. Yes, you do have to suspend disbelief, and sometimes the material comes off as a bit hokey, but you actually really care about the characters, and are just as delighted as they are when they make new discoveries, even if it is something as simple as learning the concept of laughter.
This is a really fascinating film, and it feels like a pretty high water mark to me. Some of it got a little slow for me in a couple of places, but that aside, there's not much (that I'm personally aware of) wrong with it. I thought it was pretty realistic, and well researched, and I liked that it was rather artsy and that the film had no narration (outside of an opening crawl) or real language or subtitles, forcing the viewer to follow things solely based on music cues, facial expressions, actions, and body language.
As far as acting goes, it's pretty damn good. This was probably more challenging than it might seem, but everyone does a wonderful job. At the time, none of the cast were known, but that has changed for two of them: Ron Perlman and Rae Dawn Chong. The makeup and effects are pretty decent, though I think Perlman might have been too authentic (sorry bud, I love you and your unique look, but that's probably why the types of roles you get are generally pretty limited.
All in all, this is some tremendous stuff, and it's definitely great at provoking thought and discussion. Unfortunately I don't think some people would be mature enough to handle this without giggling, and it's not for all tastes anyway, but I do think it's one that everyone should see.