NBA Showtime, Cart Fury - These Vegas games used a Voodoo Banshee video card. The current 3dfx voodoo emulation has some basic support for the Banshee, but it is pretty minimal. The tricky bit is that the Banshee (and later, the Voodoo 3) have integrated 2D and 3D capabilities, so we need to emulate at least part of a VGA controller in addition to the 3D. These boards also had some new features that require some addition internal reworking of the Voodoo driver.
Mortal Kombat 4, Cruis'n Exotica, The Grid, Invasion - These Zeus and Zeus II-based games all use a proprietary 3D graphics chip that has no available documentation. As of MAME 0.121u4, Mortal Kombat 4 is classed as working.