Once again, I agree with Derby.

But even though we are talking about engines and such, it just takes us away from the main point.

Jazz isn't an RPG or a FPS or a Strategy etc. It's a platform game, and there is no chance that a platform game will make a good RPG blah blah blah. Why do you like Jazz anyways? Did you ever think of that? Why would you buy JJ3 instead of any other RPG/FPS/Third Person that is at an even higher quality than the game in every aspect. Think about it. If Jazz 2 was a FPS game, you wouldn't think twice before buying Unreal, Quake or Half-Life that are much better games. Jazz 2 was the only platform game on the pc, and a VERY good one, and that is why you bought the game (if not then the fact that you're not playing some other amazing game out at the moment scares me).

Platform games can be 3D, Sonic Adventure 2 is a great 3D platform game (if not the best). Crash Bandicoot is another one and the list goes on. Those games still sell loads of copies and are major contributors to their publishers and the gaming market. Of course Jazz 2 has a lot more action than those puzzle solving games, but times are changing, and soon you will see players getting bored of jumping from platform to platform killing the occasional enemy and want a bit more action. It is exactly for that reason that Serious Sam was made, and why ID is making Doom 3. Epic might just take that opportunity to re-introduce Jazz, but right now it's not likely.

In the mean time (like I said already), just play Jazz 2 while you can.