The biggest issue with Crossfit (and I say this as someone who tries to make a class minimum 4 days a week) is that a good coach is 100% necessary. Our trainer walks a really good line between encouragement and respecting peoples boundaries and limits.

Some coaches at other gyms just push people too hard, encourage people to try and "push through" when they are bordering on injury. Shouting motivational slogans "No pain, no gain" and other bullshit like they are a fucking drill instructor.

It REALLY works for me because the workout changes every day and its a good mix of cardio and weightlifting, if left to my own devices I would just lift weights. Fuck Cardio. But Im there for an hour a day, theres a trainer who actually watches and makes sure Im stretching and warming up correctly and that after half an hour I dont decide "this is hard" and just fuck off home.