Had no real issues with Monarch. Yes, a low cost airline, but I don't recall any particular issues with space compared to other scum-class flights.
TBH, not really had any particular issues on any flights that were down to the airline. Have had the usual delays that we all get, had emergency landings due to onboard failures, had an aborted landing due to a light aircraft being in the wrong place, had the usual little brats screaming and kicking the back of my seat all flight, and so on.
But I'm of average height. What I lack in height, I make up for in width though.
Now, the airports. Don't get me started on the airports. Esp the UK ones. None of them are even remotely any good, but Luton must be singled out for the worse of the lot, followed fairly closely by Birmingham.