I recently demo'd Essbase through OBIEE to a client and they echoed my feelings exactly...
'The graphs, charts, etc are good - but the hierarchy is very poor'
Their main complaint was in using prompts, none of the Essbase parent, child, descendants etc are present to allow picking members, and worse yet as the list is flattened it is completely impossible to know what levels of a multi-dimensional hierarchy you are looking at. (this is true in answers also, where you need to have an intimate understanding of the hierarchy if you are to build anything meaningful at a detailed level)
Okay the dimensional columns are nice, but limited as only with a very small hierarchy do you actually want to present them the entire hierarchy and you would be unwise to present multiple dimensional columns to an end user as they are very resource hungry on Essbase.
Does anyone have any real answers to these issues?