Amount of third party integrations and modules.
Number of themes and templates.
Steep learning curve.
Now owned by eBay - makes me feel insecure as to the future of the open source model and the separation between ebay, paypal and their other interests.
Competition law issues and conflict of interests for ebay to own this sector as well as owning the worlds biggest marketplace - most magento shop owners and site operators are competing with ebay and ebay sellers - this is a serious issue.
We may be controlled by ebay and our successes dictated by their development of magento, which will inevitably be head to head in terms of priorities, when looking at the small traders.
Ebay could wipe out most competition for their marketplace if they later choose to bring magento community / open source model to an end. Thereby forcing online consumers to shop on ebay marketplace, and so ebay will benefit from commissions on sales there.
MARK MY WORDS - this will happen - and this is why they bought magento out.
This is precisely how large American corporations work - and how they succeed at dominating global industry.
Ease of use.
Administration requires complexity and knowledge and tech savvy users.
Not necessary for small shop owners who do not have IT skills or IT admin staff.
Overly complicated in most cases for such users.
Free access for the common man and everyday person ie no barriers to entry - to be able to compete with major companies, utilising highly scalable, well developed e-commerce software at no cost.