I've been using this soundcard for over 4 years now.
You seem to get what you paid for. Within it's price range, it is fine processed. Although, I would invite more quality faders. Otherwise, the connection is tough enough.
The card never did any unpredictable action ;) But you have to use quality FW cable. You may expect some problems with cheap cables. Card stops communicate.
No problem. Except working with software mixing console. The problem is, that you can't set panorama of the mono channel to the middle when using hardware monitoring. You always hear it in Left side, or right side. Not too comfortable when singin...
I solved this problem by sending the signal to Distribution headphones preamplifier and sending out only mixed mono signal. It's acceptable while recording.
Sometimes a little tricky when you want to change sampling frequency. If you find out, that you can do it by creating new project with the desired sampling frequency in your recording software, it becomes no problem.
Sound quality: Quite good. Really fine. I used M-Audio Audiophile 2496 and M-Audio Delta 1010 LT. When I bought Hercules, I didn't mention any degradation in sound quality. Actually, it was a little better in terms of noise and Dynamic range. I'm quite satisfied. Be sure to use balanced cables when possible...
I was satisfied after buying of this piece. It's mobile, it's simple, sometimes hard to monitor when recording. But still - I like it.
I think, I'm going for Presonus Firestudio Tube. But this Hercules is still good to have because of digital interfaces.