I have noticed many improvements on many games... but some regressions too. When I have a bit time I will edit this post with that regressions, maybe it can help developers to fix these problems.
Perfect dark runs really fast, but when I finish the first level, it get freeze the screen waiting to continue to the next level...and you need to reboot the game.
Mario tennis runs much better, it is almost playable and other games like pokemon stadium get fixed many of their bugs.
Congratulations to the devs for this great emulator.