I completed it on the iPhone 4 but really feel like playing it again, is it worth downloading for the iPad 2 or are the visuals identicle?
HD doesn't mean the graphics are better. Often the graphics are worse on the iPad 1 than on the iPhone 4 because the iPad 1 has more pixels but half the amount of ram as the iPhone 4. I haven't played Dungeon Hunter 2 HD, but the screenshots look similar to the iPhone version. I don't think it's optimised for the iPad 2, so personally I would stick to the iPhone version.