The first film, simply entitled Dungeons and Dragons, was an famously rubbish, medium-budget movie released in 2000, starring Jeremy Irons, Thora Birch and Marlon Wayans. The sequel, Wrath of the Dragon God, was released in 2005 and was a near-zero budget movie starring absolutely no-one you've ever heard of. Whilst the first film was awful, it did have some basic watchability (due to the excellent 'down a pint every time Jeremy Irons either overacts or looks like part of his soul has died due to the dialogue' drinking game). The sequel was fifty times worse. If the trailer is accurate, the third will continue this decline in quality to hitherto unsuspected depths.
If you want to watch a decent D&D-based movie, I instead unreservedly recommend The Gamers II: Dorkness Rising, a very zero-budget indie movie made by fans with real talent and wit, and much more successfully nails what makes roleplaying games fun.