I've done a few kits, and always enjoyed them. They had everything I needed and worked just fine.. I especially like to buy a kit when it's something I don't have much of.. like Halloween fabric.. Then a kit is very nice to do!
The thing I don't like is that I almost always want to change something.. like add an extra row so that the quilt is rectanglar rather than a square... that gives me fits now and then... so I'm careful which kits I buy..
Mostly I make up my own stuff so don't bother with a kit, but I'm glad they are offered.