For a document repository, this software is the grandest of them all. It's been around for quite a while and has had major improvements in its software. Although it has been owned by different companies, the quality has improved release after release. That is definitely something to note. Additionally the ease of use is good but nothing to write home about it. There are no bells and whistles with this software; yet, it functions great and doesn't crash unless you mess something up internally.
You have to have some major training to add any functionality like custom workflows to this product. Adding functionality is a non-trivial exercise and you should have a Documentum consultant around if you need to modify the base system.
I have been using EMC Document since more than 6 years for my organization's daily need to managing documents.
It has very good document versioning mechanism which is highly customization, it provides very good version control mechanism along with Access Control List. Also helps to enforce various policy related to document.
Document convertors and Link sharing is great features of the tool.
Documentum is best tool but it has huge licence cost associated with it. Alfresco (Open source) is also best choice if orgnization wants to get good tool with similar features.