My dad is a tree surgeon, he's self employed and usually works alone or employs someone to help if it's a bigger job. I've worked for him a few times, I don't have any chainsaw experience so I was only ever doing ground/rope work.
I can't say I enjoyed the work that much, but it was a lot better than other jobs I've done. Trees can be bastards, they love to scratch you and poke you in the eye at any opportunity, you end up stinking of moss and general greenery by the end of the day and ropes WILL catch and knot on any little branch it see fits.
Saying that, it's a good work out, its satisfying seeing a completed job and watching the bigger branches fall. I imagine working up the tree to be more rewarding but there are more risks obviously. My Dads never hurt himself with the saw but he was pulled out of a tree when his rope got snagged and he fractured his pelvis.