I've had my share of problems with Monokote over the past few years, but after trying Ultracoat and 21st Century film, I've gone back to Monokote (except for the models I paint). I think most of the problems were with quality control; you can get bad Monocote rolls, but most are OK. The earlier advice in this thread not to rely too much on shrinking it is sound; the older stuff shrank a lot, the newer not so much. Except for serious compound curves, I pretty much don't use a heat gun on Monokote any more: Just put it on as tight as you can and shrink with an iron.
This isn't meant to bash UC and 21st Century. They do go on easier for beginners. It's partly a question of how you like the different colors. And the Windex method of trimming with Monokote works really well.