MySQL has established itself not only as the most popular open-source database, but the most reliable one as well. In my more than six years as system administrator managing various websites and web servers, MySQL has been our server of choice for web applications. It wouldn't be acquired by Oracle if it did not see it that way too.What I like most about MySQL is that it's relatively easy to install, fast, lightweight and reliable. It's available for both Windows and Linux, making it a very good alternative to other open source databases back then, which only runs on Linux. PostgreSQL for example did not have a Windows installer before. This made it very difficult to adopt it for mixed-OS environments and that is why we use MySQL.
Room for Improvement:
Back in the days, our only gripe about MySQL was that it was a purely command-line based system. We don't really see it as disadvantage though, as it allowed it to be fast and very reliable. This has been addressed through the years with graphical management systems for MySQL. MySQL is a highly recommended product. I give it five stars as it really gets the job done without much of a hassle. Being available for the many platforms also makes it a very compelling choice for mixed-OS environments, as data migration can just be as easy as backing-up and restoring on another server even on different operating systems.
Just be ready though to work at the command line should you wish to use MySQL in its free form. It may not be the most intuitive user interfaces available, but it also makes MySQL a simple yet very reliable database for most people's needs.