Personally, I hate bash. Besides having syntax which is totally foreign to me, which I forget every after every time I attempt to learn it, it is extremely slow.
Besides that, I like structured data in the form of an object vs parsing everything from text.
However, this really is more of a unix criticism and less a bash criticism.
You use something like bash or zsh when it is convenient rather than to actually do anything with. If you are finding it slow use python, perl ,or something else to do your task; the real power of the shell comes from the easy access to all the unix tools that work well for their singular tasks. That power would be the main criticism I would find with the ruby shell, it seems so foreign and without access to the tools available (unless of course it is using them on the backend) but piping and other one off things would be interesting to see as examples because right now this shell looks like ruby with some libraries added in (sorry not a ruby programmer so I don't know the proper term)
I agree with your comment about structured data. Parsing everything from (unstructured) text is pretty backwards, it's more work and very error-prone.
But calling bash slow is kind of strange. What are you trying to do in a shell, that you can call it slow? A shell simply parses commands and dispatches them. For example, if you grep a 100GB file and it takes a long time the shell is not the bottleneck.
Why are people approaching a task which has a prerequisite of being speedy with the shell in the first place?
My only complaint about modern shells would be the lack of data structure support. I think it's slowly being remedied what with bash getting basic associative arrays.
