Ah yes LN2... the game simply isn't finished. Once you take a good look at it and you examine the actual levels, you'll see shadows with no trees/bushes, missing elements that are there in the C64 version, etc. If you examine the animations (and I have done so extensively...), you'll find missing frames or even animations with two frames switched around.
IMO they ported the game and the release was rushed before an optimization could be performed. There is simply no reason why the game has to be that sluggish.