They are just an appalling operation, and they're not always cheaper. There are various European destinations where they'll beat the pants off of BA, but it's surprisingly less frequent than they'll have you believe. Especially when you consider that their advertised fare will be a 5am departure, or similar, from somewhere like Stansted (which will entail a taxi fare out there at that time of the morning), and a country-train or bus service from your destination airport into the city.
Once you start factoring in a departure from some horrid airport in the English midlands (purported to be "London" though), arriving at a satellite airport equally remote to your intended destination, and the fact that you'll need to be out of bed at 2.00am for the privilege - oh, and hidden charges like £10 per check-in bag, £2 or £3 if you don't have your e-ticket printed, £10 if you want an allocated seat, and their latest great idea to charge you for use of the loo inflight - and you'll realise, like I did, that the whole thing is a charade.
There isn't even the pretense of customer care. They closed their customer service desk at Stansted and replaced it with a premium rate, time-charged phone number.
So when you join the queue at Stansted two-hours out - as they demand - to check-in for their first flight of the day to Berlin, as my colleague once did, and find yourself second in line when the clock strikes t-minus 40 and they close check-in on you, you can spend forty-minutes on hold, paying Ryanair for the privilege, to ask them to rebook you on another flight on account of missing your original one because their business model doesn't provide enough check-in agents to deal with the number of tickets they've sold.
Ryanair's take is that you're paying "rock-bottom" so you don't have the right to expect anything more and you should bloody-well shut up about it too. They didn't even bother responding to a British government questionnaire sent out as part of an "effort to improve the air travel experience" of the British public.
I grew to despise them enough to choose another carrier every time, even if it meant flying in to the nearest town and catching a train for half an hour.
A Ryanair horror stories discussion on here would be a long thread.