I flew Ryanair twice in the last two days and in fact I just got off the second flight a couple of hours ago.
I only chose Ryanair as they were significantly cheaper than all other competition. As in, I paid ~€20 each way when the next cheapest option was over €100. Ordinarily I would not use them but this was an exception.
Do I regret flying them? Well, I am undecided to be honest. I really didn't enjoy the experience but they did get me from A to B on-time with both flights and I did save a lot of money. However I didn't book any of the extras, such as baggage, food, seat selection etc. and I checked in online. Had I needed to pay for too much extra the price difference would have narrowed and I would have considered taking a "better" airline.
To answer your specific questions:
1. Check-in. DO NOT check in at the airport. The airport check-in fee is €70! If you check-in online but don't print a boarding pass, the BP issue fee is €15 - more reasonable but still crazy IMHO. The solution is simple - check in and print boarding passes before you get to the airport! You can do it IIRC up to a month out. (It may be a week - don't remember exactly but it's a decent amount of time.) Even if you pay the Business Plus fare which includes airport check-in, you will have to queue up with all the people checking in luggage. In BCN, that was a ridiculously long line. Although if you are checking in luggage anyway, that's irrelevant.
Oh, and one other thing, you will need to go to the desk/ticket office to get your passport sighted and BP stamped once you arrive at the airport if you are travelling on an Aussie passport.
2. Boarding: Boarding those Ryanair flights was NOT my idea of fun. At the very least there are allocated seats but everyone still seemed in a rush to get on before everyone else at any cost. The advertised "Gate Closes" time came and went and the plane hadn't even arrived at the gate yet. There was a very long line already by the time the plane got there. If you have fast-track boarding or whatever they call it you will get to board with all the other priority boarders - on my flights there were about 3 dozen. At least you should get overhead locker space if you do this. But it will most likely still be a scrum.
3. Seating comfort. I'm tall and found it barely tolerable. The seat pitch is pretty minimal unless you get row 1 or an exit row, which seemed okay. The seats themselves seemed okay but not the best. No seat pocket to store anything. On the first flight, the floor around my seat hadn't been cleaned properly so lots of crumbs etc. all around my seat. The second flight I ended up with a middle seat as the flight was completely full and nothing else available - frankly, it was not experience I want to repeat. Also, on the second flight they dimmed the lights for take-off and when I tried to turn on my overhead reading light it didn't work at all. Not a big concern but if they look after the rest of their aircraft in a similar way I would be worried.
I think you get the idea - I didn't really like Ryanair. They seemed to spend half the flight trying to sell things too, which I just found annoying... everything from food, to perfume, to scratchies, to bus tickets. However I would fly them again if the saving was worth it.. and the flight was short.
But TBH if you plan to spend the extra money on a "Business" ticket, you might as well just book a good airline and have a much more pleasant flying experience.
