It was made for kids and teens of the late 80ies or early 90ies and as such it was truly a film of it’s time. If you hated that period, or love the first movie so much that you can’t even take a joke about it, then this is garbage, but only because it wasn’t meant for you. The low budget here and failure of the Beastmaster 1 at the box office (grossed under four mil. with a nine mil. budget) were obviously the reasons to drop the seriousness of the original and to put it in the present day. You can complain about the story, dialog or logic, but again this was made to run, not to win races. If the movie had tried to take itself seriously it would be a total failure, but it doesn’t do that for a second (in “our” world, Dar sees a movie theater that’s advertising The Beastmaster 2, enough said). To paraphrase Clint Eastwood from Dirty Harry movies: This movie knows it’s limitations. It’s more of a comedy/parody then usual adventure. Soundtrack (for the time) was also great. Actors aren’t taking themselves that seriously either so even the usually irritating “spoiled rich brat” role (played here very well by young Kari Wuhrer) turns out good.
So, if you are nostalgic for the 80ies/90ies (cheese) culture, or you liked the first part, and don’t mind going out on a cheese limb, you’ll have tremendous fun with this attempt to revive Dar in the 90ies (literarly). This is not really the sequel to the first, and don’t watch it if that’s what you want. It’s more of a “what if” fantasy sequel.
As for the “why different dimension and not just different time” question: When in history did we have those tall winged humanoid creatures that suck the flash of bones (from the end of part 1)? By the way, the movie ends in the Zoo because of an attempt at a cheap (moneywise) big finale. It’s suppose to be the best place for Dar to show all his moves (him being the manipulator of animals).