As a developer with several years of experience working with different WCMSes, and now having implemented several sites on the Vertical Site platform, I am very pleased with this product.
About the company, Enonic have a strong technical support throughout the company and support is local and very fast for me & clients on the Scandinavian market. Concerning Vertical Site, they have a well-conceived and solid product release plan, and the product has become a very mature WCMS that can also be used in part with other portal products.
Highly customisable (whether by working with the flexible pre-defined data sources, or developing external components for integration), based on open standards/technologies such as Java, XML/XSLT and possible to deploy on several platforms, I've come to learn there are very few technical issues that cannot be solved on Vertical Site.
Vertical Site's strong separation of content from presentation also enables content editors to quickly get up to speed on delivering content and similarly gives developers full control over the presentation framework, and although the learning curve at first may appear steep, the product is intuitive to work with for both technical and non-technical people and comes bundled with detailed documentation covering most aspects of use.