For those clients that we've worked with, EPiServer is primarily being leveraged by an organization's Communication/Marketing Department as owners of the system (and then supported by Experis or internal IT staff). The immediate pain points that it has been able to address is the ability to manage the publication of content and new pages without having to rely on other resources bandwidth for assistance.
Innovation - EPiServer is constantly looking at ways to improve their product and partner with organizations that can develop add-ons to improve the overall features of the core platform. For Example: SilverPop (marketing automation) and Celum (digital asset management).
Content Management - It may seem obvious that a WCM product should manage content/reuse well; but, let's be honest, not all products do what they claim to do well. In this case, EPiServer understands the core functionality and has created product that is intuitive and exceeds customer expectations in this area.
Previews - EPiServer has built-in templates (emulators) that allow you to easily confirm how your content is going to be displayed on a variety of devices before you publish your content. This is advantageous as it eliminates the guess work and need to redo content (or even code) after you've gone to production because you weren't able to thoroughly test it before hand.
Translations - When we first started to work with the product, the platform was missing the basic ability to export/import XLIFF for translation companies to leverage; and, it relied on developers that had created an Open Source module called "Translate X". The module was buggy, version specific and had little to no documentation. Since then, EPiServer has partnered with other software/translation companies (IE: Translations.com) to improve this experience; however, I believe that there is still room for improvement and other options.
North America User Conference - Adoption for EPiServer is growing in NA; and, there are more partners than before willing to help with your specific implementation. One of the things that I would like to see is an annual conference where the community can come together, publicly discuss their pain points, success stories, conduct demos, talk about the product road map, etc; and, would be similar to what other competitors (such as Sitecore & Ektron) do.
Time-to-Market: For our clients that are on the EPiServer platform, they are able to quickly create content and push it to production easier and faster than in the past; and, part of that is due to their intuitive WYSIWYG Editor.
Content Migration: For our clients that have moved from a different CMS platform to EPiServer, the content migration effort itself was much more efficient than previously anticipated; and, thus created a cost savings for the client and accelerated the project timelines.
I believe that EPiServer is here to stay; and, we routinely see them competing against other similar .NET technology platforms in this space (IE: Sitecore & Ektron). Experis has been following the Gartner Magic Quadrant and Forrester Wave reviews; and, EPiServer is well positioned to move into the "Leaders" quadrant in the near future (as of the 2013 Gartner Magic Quadrant, EPiServer was listed in the "Visionaries" quadrant).
As an implementer, Experis continues to recommend/support EPiServer as a viable CMS platform and we do not have a direct renewal scenario with EPiServer ourselves. That said, we do have indirect ability to influence existing customers (as a trusted adviser) on their annual renewal; and, there are no existing clients/scenarios in which we would recommend them leaving the EPiServer platform.