I think the game mechanic is very appealing to most programmers because the underyling mechanics are pretty easy, because the game world is very constrained and tile-based. Making it pretty is also not so difficult, given a good and talented artist.

Making it fast is a completely different story and requires lots of indian rope tricks. You can't blame Gamestudio or any other engine for not being fast enough for this, because they weren't written for it. Plus, the graphical detail used in the original game (in 1997) was very poor:



My guess is that they dynamically created, changed and skinned the 1) upper, the 2) lower and one or many 3) wall meshes. All other static 3d objects might be baked into one mesh, too and all other entities are animated sprites (sic!).

[EDIT] It also seems that they precalculated the lighting and put it into the vertex data.