I've flown then four times and all flights went without a hitch. Considering I only paid something like a £1 for each of the flights it's no wonder my opinion is good.
However that was a long time ago so things might have changed especially the extra add on costs which didn't seem to be so much in evidence back then. The only regret I have about Ryanair is the fact that they weren't around when I was a young financially embarrassed backpacker.

I would never pay big bucks to fly with them but would if the price was reasonable enough.