I’m just curious, but what does that end up meaning in a practical sense? It seems like some games work better than original hardware, while some don’t work at all? Are there any glitches in games? Especially graphical ones? (That’s mainly why I don’t like software emulation.)
FPGAs are the exact same thing as emulators though. Some of the inner workings and methods of emulating a system differ and it's more efficient to do it on an FPGA, but the accuracy and compatibility still depends on the developer knowledge, experience and skill.
This particular FPGA have reached a "wall" with the current chip where the developer can't improve it much further. It needs a better FPGA chip to go any further, along with more research and testing. Because the last few issues (that are mostly about timings and making some of the harder to emulate games work) are also the toughest and that's why you don't have a perfectly accurate N64 emulator yet.
The core's current accuracy/compatibility status is not much better than any current emulator. It's actually kinda worse in fact.
The bugs and inaccuracies you will find are very similar to older software emulators like Mupen/PJ64. The games that do work may have timing and speed issues. So it's not only the few games that crash or don't boot, a very large amount of games that do work are not running at the correct speed, even in the non-turbo core. If you want correct timings, you are better of with emulators such as Simple64 and Ares, both more accurate since the developers are focusing on fixing timings, specifically, for a few years now.
The "Turbo" mode is basically the same thing as the "counter-per Op" option in Mupen (and there is another one for PJ64). It messes with the timings even further to push the games with unlocked frame rates to run smoother.
