I'm working for about 3 years with Magento CE now. I was only working in 2 different projects but my last one, I'm still working for, is getting big and I'm leading the development.

I can understand both sides. Magento provides alot of features and it's possible to implement almost all custom stuff. But in the end your not always able to add them. Adding to much features will slow down Magento too much. Magento is already very slow. And thats also a problem with the community extensions you can buy. They just don't care about the performance. It's not only a goal to implement a new feature, it should work without loading all stuff again from the db no matter how much resources it costs. Whem I' thinking about all the servers we added for this xmas time to handle the visitor-peaks...

And ya, some templatesfiles are really a pain. The example of the price.phtml is showing very good whats wrong. XML, well it's ok because it's possible to create any kind of page even from the backend.

If I would start a new project, I'm not sure which other software I should use. If we need alot custom changes magento allows use to add them without breaking the core.

I hope magento 2 will improve some of the main issues.