the 3rd one in 2015 after Heathrow and CDG. As you point out, it is already saturated but funny thing is that contrary to what happens usually the issue is not one of takeoff/landing capacity but one of size of terminal buildings capacity
That's exactly what's happened. It's stuffed with people. One downside is that connection times are a problem since the queues for security for transfer passengers can be a nightmare, especially in summer. This mean people miss transfers they've been sold and have to be put on later flights (and their customer services are crap and chaotic) and this just ****** people off and creates more problems later. I can't abide CDG by the way, it's even worse than Heathrow which is bad enough.
Poland is fine at the moment. Ryanair's hub at Modlin is tiny though and never intended as a hub. If Ryanair want to do more with it, they'll have to sort something out for transfers plus there need to be lounges etc. For domestic travel it's OK. I can see Okecie reaching capacity soon, too.
I used it last year Modlin-Bristol and it was great. It cost about 80 GBP return. Yes, if passengers can't follow simple instructions and print their documents, they get hit with a surcharge. It's a stupidity tax
It's OK for short hops especially if you get priority - makes the queuing (bad at Modlin) a bit more bearable. You don't even need to print the documents on Ryanair - you can get the boarding pass sent to your phone. A pain for connections though because of the Modlin thing, and other low cost airlines like Wizz, Jet2 or Air Baltic always seem that bit better.