What does the company do well? It does well in providing you standard e-commerce features you would expect tailored for small to medium online businesses. Good UI and UX, but themes and layouts can be improved.
What does the company not do well? They can improve on support and update their module layouts. Support is minimum because it's open-source. Should implement more drag and drop features so non-coders/designers can use it with ease.
What do you wish you had known about the company before using? I wished I had known what level of skills that it requires to run it, I've developed some sites with Opencart for clients, but some of them say it's too complicated to use, because parts of it require coding knowledge to change things around.