Do not judge a product by its cover is an old proverb and for movies it summarises to Do not judge a movie by its trailers.
The above very much applies to 10,000 bc. Trailers are impressive and add to that it comes from Roland Emmerich who created a very commercial but watchable Independence day and more impressive Day after Tommorrow.
He miserably fails this time. Some times it feels like B grade or C grade movie but saved to some extent by good special effects. The acting is amateruish as well the execution of a predicatable story.
I give 1.5 out 5 primarly for special effects