It's been a while since I played any serious paintball, but to me the biggest downside at the time was the arms race. Obviously the tippman full auto was banned from competitive play, but after that it was pretty much up to your wallet. I remember getting my Bob Long Autocoker and feeling invincible. Then some guys started showing up with Angels and holy crap I was intimidated. Compressed air vs CO2. Quality of paintballs. Even some of the gear with neoprene to give you a bit more 'bounce' it all added up.
Paintball was the most fun when we started, everyone with a tippman rental.
After our group started diverging on total spend it because obvious it was getting unfair. Eventually we all bought tippman pro carbines and required the same paintballs be used and all on CO2. Not getting CO2 freezing was part of your strategy! We had much more fun after we removed the arms race, even at the expense of not being able to tinker and customize.
The Angel guys could go to pub games and light up the poor schleps if they wanted :P