X-cart uses Smarty Templates in a PHP environment which means there are many developers who could probably pick it up relatively quickly to provide new features. The smarty template engine is very robust and well documented, and the cost of x-cart is very low which makes it easy for anyone to get started with their e-commerce business. It is a really great e-commerce software and suitable for every business. I actually cannot find any serious objection to what it does. They regularly update it, add new features, fix flaws, offer support. The software itself offers many integrations for shipping and payments, everything you need for sales. Although it covers many things, there will always be something missing, because many things happen in between customer visit and final delivery. Therefore, if you plan to expand your business, also plan to expand your X-Cart - but do not worry, it won't be hard.
For everyone. From small to huge business you get everything out of box. Just setup company details, payment and shipping methods and you are ready to go.
Upgradable. There are many plugins one can integrate with X-Cart. Over time, many of them became part of the software, and you are one click away to enable them.
Well organized code. It uses Smarty template engine, which I find great, specially for debugging (famous Webmaster mode).
Creating new plugins the way X-Cart wants is maybe not complicated, but hard to implement because there are no hooks. One has to manually change each file. This is similar to patching the core and therefore one has to know basics of web development.
Even if you get everything styled correctly with base skin, there is a bunch of unused styles you have to cope with. Start skin should be much cleaner. You may find thousands excess lines of code.
Flexibility in presentation as well as functionality
Full open source software allows for unlimited possibilities with the store function, though some developers who create modules do encode their modules which have errors in their code which therefore can't be fixed
A fully functional professional level application at a fraction of the cost of similar applications such as magento.
