I've now flown it twice while in Europe in the last few months, and have a couple of observations that may be of use to U.S. travellers in Europe. Both times, the flight left and arrived on time. Baggage arrived on time as well. As long as you pay in advance for things like a seat and "priority" boarding, you can be sure of a fairly peaceful boarding process and of having room to store your carry-ons and a pleasant-enough seat (the absence of anywhere to stuff a newspaper or magazine in a seat pocket is a bit annoying, however). The one thing that I find really irritating is that the entire flight is an ongoing advertisement for products: duty-free stuff, liquor, fragrances, cigarettes and on and on. And anything you want to eat or drink that you didn't bring on board has to be purchased, but the prices are not particularly extravagant by airline standards. RyanAir's biggest advantage is a lot of direct flights in Europe, and from airports that most other major airlines don't utilize (e.g., East Midlands in the UK).
Curious if European readers, who probably have more experience with RyanAir, have different experiences.