Ryanair gets a fair amount of bad press as an airline. Obviously this is mostly related to it being a budget option that provides really no extras with your trip in exchange for having low fares.
We recently flew Ryanair between Brussels and Edinburgh and honestly didn’t find it to be all that bad. We’ve flown other budget airlines in the past, mostly Frontier and Spirit, and found Ryanair’s service to be comparable. I would say it was better than Spirit, but I only have this one data point for comparison, while I’ve flown Spirit several times. One thing that seems to get a lot of attention is Ryanair’s cabin baggage policy, which is somewhat restrictive, but not unlike other budget carriers. Again, we had no issues and found that nobody was really paying that close of attention to baggage sizes, despite all of the dire warnings found online that try to scare you with threats of extra fees. Of course, none of this means that you might not some day have your baggage size checked carefully. I’ve just never had it happen with Ryanair, or any other budget airline for that matter.
The only real issues we experienced were first, that Ryanair flies out of Charleroi airport. This means that you have get down to Charleroi from Brussels to take the flight. The most common way to get down there seems to be the Brussels City Shuttle operated by Flibco, which itself gets a lot of mixed reviews online. We found the shuttle to be rather convenient, and because we purchased our tickets well in advance, we only paid $15 for our family of four to ride.
The other, extremely minor issue, was that the Ryanair staff at Charleroi didn’t speak any English and thus couldn’t answer the questions we had about our gate checked stroller and car seat. However, since we were in Belgium, the onus is probably more on me for needing better French.