It's an old-school enterprise CMS. And a crummy one. It's done a pretty remarkable job of staying relevant all things considered. The current market leader in this space is Adobe who own AEM and bought Omniture years ago so they can offer analytics and A/B testing in one bill of sale. Episerver must be working to position themselves the same way.
Lot of big enterprises buy these kind of systems and pay through the nose for them.
Episerver for a while was one of the main competitors of Sitecore in the IIS/.Net Enterprise CMS space. Both were European (Swedish and Danish respectively)
I built sites with both back in the late '00 and while Sitecore was marginally better I don't miss working with either.
Adobe also bought Magento, while not as bad as Omniture, has it's own levels of hell.
Lot of big enterprises buy these kind of systems and pay through the nose for them.