While the CGI effects are undeniably impressive, the laughable story line, risible dialogue and cheap humor (most of it involving a hapless zoo security guard) seriously detract from the fun.
You don't have to hand the folks behind Dragon Wars much (the acting, directing, costumes, editing, props, music, etc: They're all off). But when they decide to sic that giant snake and those prehistoric dino-birds on downtown Los Angeles, the movie turns shockingly watchable.