If you need any help with model creation, you encounter any issues, have a suggestion let me know.
You are right. Cubes, dimensions and the logical model abstraction is the very first step: physical data implementation is hidden. Cubes is young, as mentioned in my comment - front-end helpers will be coming later. I will need some help on that part.
I am not quite sure about the "feature-richness". Yes, it might sell - in environments where people barely notice wrong data in 40-page monthly report, still being content about the report exhaustiveness. From my experience, many people want just basic stuff. I am trying to make cubes as small as possible (but not smaller), however extensible. For example, the cubes will not force you to use "cube's" way of drawing charts. It will provide few examples, based on common, accessible visualising backends. Along with the examples will have possibility to plug-in your own visualisation/reporting method.
The intention is not to create competitive product to the "big ones", it is rather to create light-weight, customizable alternative for many smaller projects.
Cubes aims (at this moment) rather for tool for tool creators than tool for end users. But you never know, how the wind will change... :-)
On the front end, they only have excel, which is good, really good, but other tools have much simpler and in my opinion better clients, for example Cognos and BO
Palo (a competitor to Cognos TM1), in particular, is really nice. The other two leave a little to be desired on the UI side.
Currently I am working with a combination of PostgreSQL and Tableau, and find it a nicer environment to work with (coming from a MSSQL shop). I do not have the same automated aggregation engine supplied by SSAS, but Tableau in part makes up for that with visualization tools that require no coding on the UI side. I can focus my efforts on the data layer.
The more open source tools we can get that can begin displacing products like Cognos and BO, the better.
One here. Very interested to see this project evolve.
 p.s.: I am the only developer so far, and I am open for collaboration.