What does the company do well? Great website performance, top notch technical support, excellent site security. It's truly a case of you get what you pay for. WPEngine costs considerably more than other hosting providers, but along with that comes the performance and customer service that's considerably superior than the competition.
What does the company not do well? Several Wordpress plugins are restricted from WPEngine, in the name of optimum performance. As such you can't install (or least leave installed) plugins like UpdraftPlus, broken link checkers, and other resource-intensive plugins. This may or may not be an issue for you, depending on what your needs are. If you're migrating a site, confirm that your plugins work on their platform.
What about the company do you wish you had known before purchasing? That certain WordPress plugins are restricted from the WPE platform.