Microsoft Outlook is full of far more features than most email clients. I really like being able to set automatic replies when I am away from work. I like the number of plugins compatible with Outlook. If you have a Microsoft Exchange inbox, Outlook makes it very easy to set up your email, without having to deal with POP/IMAP settings. The ability to share contact groups among other employees comes in very handy. Most importantly, at least for our company, it can store an extremely large amount of emails before causing the software to become unstable.
Outlook is not without its problems. It tends to be filled with randomly occurring bugs. I often have to use the inbox repair tool provided by Outlook for our employees. Some are caused by overwhelming amounts of emails being stored offline, which is understandable. Often, however, other bugs appear randomly. Sometimes Outlook is just suddenly unable to start, despite not having to load a large amount of data and requires the use of the inbox repair tool. Most recently I was unable to make an employee's laptop able to send emails until I downgraded him from Outlook 2016 to 2013. The support for problems such as these is very poor. Asking questions on the Microsoft forum often results in a generic list of things to try that any IT Manager would have already thought to try. One last point of criticism is Outlook's handling of POP3 protocol. Many users who were originally connected to Outlook via POP3 noticed their emails would come in bunches, rather than right after they were sent. It's hard to say how much of that is Outlook's fault, but certainly if you are choosing to use Outlook, I would recommend IMAP and Exchange over POP3. Overall, Outlook is a terrific tool, but it would be greatly improved if Microsoft took more time to address its bugs as well as provide better support to their customers.