I've found that other than the camera angle, Yaksa (yeah, I said it) has virtually nothing in common with Space Harrier. That said, I still enjoy it. I still haven't beat it, but I haven't played it in a long time, either.
Space Harrier is a static shoot 'em up that calls for very little strategy, Yaksa is an into-the-screen platformer that requires lots of planning, practice, patience and memorization. Not to mention the gameplay is much more dynamic. My initial attraction to the game was of course it's superficial similarity to Space Harrier, but it became clear within minutes that it was a very different affair.