I've had both knees shredded and reconstructed.
The surgery part is pretty easy. I opted to stay overnight in the hospital both times, but they'll let you leave after you wake up if you want. Also, if they suggest you rent a machine to move your leg automatically while lying in bed at home -- pass. It's not worth it.
Physical therapy was a big m-f'ing bitch for me. There's one day that comes along where they just lie on your leg and bend your knee for you, and you'll literally be screaming as the scar tissue rips. So, you've got that to look forward to. OTOH, I haven't stopped being active even with both knees done. I played soccer for years afterward and I've been downhill and water skiing, none of which is recommended. I've also been able to run again, but not more than 3-4 miles max. Your knees will always be sore after exercise, but you get used to it and it's nothing a little aspirin doesn't resolve. I did pretty much stop playing basketball and tennis, though. Too much torque.
P.S. Empty your bladder and bowels thoroughly BEFORE the surgery.
Good luck!