Important ammendment to my previous review! I have been able to make some games work *perfectly* that I previously may have mentioned as "technically working, but not really playable." I'm talking about major games, some of which made the N64 popular and definitely make this emulator an incredible must-have fun item.
Off the top of my head, I have been able to get GoldenEye, Diddy Kong Racing, Perfect Dark (#1) working perfectly, with NO graphics or interface problems. Again, these are only three that I can remember. There were others, and you should try your own collection! Sound may still be problematic and a bit skippy on some titles, but I found that disabling in-game music works most times. Otherwise, try toggling the "enable audio plugin" setting (or, worst case, just toggle the entire "enable sound" setting). But a fair number of these games run perfectly otherwise.
In every case, try running the ROM again and again with various settings on/off (i.e. audio plugin, expansion pack, speed limiter, and the big one that helped me make major games work: multisample level, under graphic settings). Also, no matter how sure you are, make sure your game ROM works. I found one or two ROMs were faulty, nothing to do with Sixtyforce whatsoever.
I'm having a lot more fun, and this thing is worth the money, easily. Sure, it doesn't work with everything. And it needs a bit more smoothing with regards to the audio plugin, but I've never seen an emulator so robust, stable, and functional. You just have to be willing to experiment with the settings (sometimes even the settings that you don't understand and are really apprehensive about touching!).