With great customizability comes great responsibility
I like the product a lot. It is extremely customizable. That's wherein the trouble lies I think. We've not had so much trouble with the core product, but with customizations. It is really difficult to tell what potential problems you can be introducing down the line when you stray from baselineI think we lack the staff required to truly manage it as well as it should be. Every upgrade requires a lot of testing, and you never find everything it seems.
Another complaint is that a few of the modules are not developed as thoroughly as some of the more core modules, so if you really want things to work for you in those areas, you're almost definitely going to be doing some customization.
Be cautious, very very cautious. When you customize things, expect the returning cost per upgrade to be almost as much as the original devlopment cost.