Space Harrier 2 doesn't break any boundaries, and only ends up being a marginal cookie-cutter of the original game.
Space Harrier 2 shares many similarities with the original game. As a matter of fact, it makes you wonder if the game itself really is a sequel. Many of the game's levels appear as if they were simply cut and pasted from the first Space Harrier and had their names changed. The same holds true for most of the enemies. The only major difference is that Space Harrier 2 offers more levels than the arcade game, and new boss monsters--like a creepy worm with a Medusa's head, a face that breaks into four parts and a lightning-fast winged tiger.
Hardware limitations notwithstanding, Space Harrier 2 runs at a brisk pace--even though it isn't anywhere near the quality of its arcade counterpart. Yet expect to hit your fair share of trees and rock columns because the 3D is as fast as it is clunky. The music is delightfully weird with one lengthy song played at different intervals in different stages--just like in the first Space Harrier. Even the sound effects are taken from the original game--including the ever-so-annoying moan you make when you lose a life, which sounds even worse here than it did in the arcades.
Overall, Space Harrier 2 is a decent game, but it could have been so much more. It might have benefited enormously from different gameplay variations and more variety in its levels and enemies. Most sequels typically fail to be better than their original sources, and Space Harrier 2 isn't likely to buck that trend.