Funny how people have such different perceptions... HK has been great for us, we get compliments on our sound all the time.
We did play a Freshers Ball at the University of kent in Canterbury, that had an installed HK rig that looked the buisiness but sounded awful.... The reason wasn't that the rig itself was bad, the installers had compressed and limited the life out of it to protect it from Numpties who didn't know how to use it. Unfortunately it was all locked down and I couldn't access the settings to change it.
That is another point, you could spend a fortune on a good "seperates" rig but if you dont know how to set it up properly and tweak it, you wont get the best out of it and still end up with a bad sound.
The beauty of powered systems is that a lot of the tweaking has been done for you, OK you can't adjust it but its always worked for us and I've never had to adjust it other than a bit of EQ. As with reliability, OK if the amp in the sub blew, we'd be a bit stuffed (probably use monitors out front to save us and get it fixed for the next gig) but in 4 years of regular gigging, never had a problem.
If I were you, keep it simple until you really understand about bi amping, crossovers, limiting etc..... Good sound reinforcement is an art form in itself......
Good luck
*BJ*