Before barre, I was doing heavy weights, almost exclusively Cathe. However, I did dabble in P90x and a few others. Eventually (and I don't know if I can blame it on those types of workouts), I developed a muscle imbalance that led to knee pain (in both knees). So, after correcting the knee issues through physical therapy (and foam rolling), I was determined to get back into exercising.
It was at this time that I decided to give barre a try, mostly because it seemed "gentler" and I really liked how Burr Leonard emphasized that she worked the knees from all angles, thus avoiding the very type of problem that I had developed. Well, after my first few months of barre (mostly The Bar Method and Fluidity), my knees were MUCH MUCH better and I had fallen in love with the technique.
From there, I moved on to more advanced, faster-paced workouts like P57. I was officially hooked after that.
I've stuck with it because of the results: No more knee pain. A tighter, lifted seat. Muscular, but lean quads. Sculpted, but not bulky arms. All this, PLUS a level of flexibility that I've never had before. Can't really beat all of those results. Plus, the workouts are fun and not at all dread-inducing for me.