I've been doing Crossfit for about 2 years and I love it. That being said, it's not a bodybuilding program and its not a marathon training program. It's designed to fall in the middle and targets overall conditioning using a lot of functional exercises and a combination of lifting/strength stuff, gymnastics, and met conditioning.
The workouts are short (usually <30 mins) but kick your ass. They are usually a workout that you do within a certain amount of time (AMRAP) or a set workout that you are working against the clock. Most CF gyms start with some sort of strength workout (deadlifts, presses, C&J) or a mobility type workout too. You're generally done in an hour.
The only two things I would suggest (like those above) are:
1. Take the time to learn the moves and dont worry about weight or competing with others, just yourself. The community is generally supportive and I found that I never get bored like I do working out at a gym. It changes constantly.
2. Do your research and try out a couple different boxes (gyms) if you have them around. Each one is different. Ask the trainers about scaling and tailoring workouts to your abilities to start. They should be receptive to that. If they aren't I'd be careful.
Again, people have very different perspectives on Crossfit. I've found I need to combine it with other things (lifting, triathlon training) to achieve what I want. Also check out the website. You can do it for free, but there are benefits to joining a gym (thought it can get expensive).