PrestaShop

This has been a great solution for medium brands that process more than 100 orders per month and have some particular functionalitys of management stock with third party shared integrations

I have three stores now with Prestashop, which I have been using for over six years. I would say that the older versions worked perfectly well and I had no problems. I would have given 5 stars in all areas. (I am talking version 1.6.0.9 or thereabouts)
Unwittingly "upgrading" to the latest versions, I'm now on 1.6.0.14, has rendered Prestashop almost unworkable. It only works now for me thanks to the brilliant paid add-on Store Manager.
My two sites with fewer products - 20 and 1200 respectively, work fine still.
My main site, which is my main source of income has 4,500 products. I cannot edit or save products (which is where Store Manager comes in). The search indexing does not work. CSV product import will not work. Database backups always time out. There are frequent errors with Payment gateways. Every recommended update usually causes new problems.
All this despite the fact that I am using the default template and have made no code changes.
Support is absolutely zero. My problems have been well discussed on the forums for over two years and are common. The programmers do nothing. I am not a programmer. I have spent over $2000 on programming help over the last two years just to keep my site running - and Prestashop is supposed to be "Open Source" and free.
I would highly recommend Prestashop if you have few products, but I would say that if you start to go over 2000 then in my experience it simply does not work. The programmers are too busy making add ons which they make money on, than getting the basic shell to work.
Transferring to another cart now would be a nightmare, largely because of the huge number of product photos, I think about 30,000 now.

Overall besides upgrade issues, this is still the best ecommerce building site. It works globally and offers you everything you need from the default package.

It is good when you start your online bussines. A lot of free and paid templates makes easy to choose preferred design. Almost every payment gateway in the world has a dedicated gateway for PS so you may start your online store in few minutes. But when your shop will rise - it is hard to scale. Especially if you want to integrate it with some external apps (like 3d shopping) - you may hit the wall here. Communication between plugins may slow down your store so it wont be rocket-fast anymore.