People seem to have a love-it-or-hate-it relationship with the e-commerce module. We (furfly) have used it on several sites and it has been fine for what we needed to do. Others have fought with it every step of the way and have declared their, err, distaste for the experience. I think it depends greatly on how close it is "out of the box" to what you want to do. It's not very flexible, so if you need to make more than superficial changes you'll be getting your hands dirty in the code, and how fulfilling or frustrating that turns out to be depends on what you're trying to do.
I'm not sure if that shed much light on the subject, but that's my $0.02. :)
Good luck!
