Why is my computer so extremely bad at handling NES emulators?

[*Laurelindo*]

This is ridiculous.
I have tested countless NES emulators for like 30 minutes now, and they all have some lame flaws that make them useless.
Either they have bad sounds, cannot load Full Screen, have bad colours, play the sounds too quickly, or simply refuse to load in the first place.

The only emulators that seem sensible so far are FCE Ultra and Jnes, but - yes, they also had flaws.
FCE Ultra cannot show Full Screen mode ("DirectDraw: Error setting display mode" yadda-yadda) and Jnes is bitching with me - it plays sound fine on American versions, but refuses to play it on Japanese versions (and I wanted to play Dragon Quest in Japanese ).

Why do they suck like this when every site boasts about how awesome and compatible they are?

I used to play on NesTopia, but that emulator has started to have some serious sound issues lately and constantly slows the sound down, then quickly jumps back in sync all the time which is really annoying.