What do you like best?
Multi os support, easily expandable , granular access control. Data can be distributed by nodes type based on performance needs.
Scaled out architecture that can be upgraded with no disruption.
Supports multi protocol.
What do you dislike?
Might be too complex for small environment.
Where a smaller nas might fit better.
Could be expensive sometimes.
Recommendations to others considering the product:
I recommend using ISILON if you have a dvr like environment which generates lots of data.
It is very Useful as well in case of data consolidation, so if you have many silos of linux, windows old servers and old nas that you want to get rid off. Isilon would be your best fit under to put all this data under one namespace.
What problems are you solving with the product? What benefits have you realized?
Organizing Unstructured data. ACL very granular, you can give access to users based on active directory groups or to which network segments etc...
Isilon scale out easily in size and performance.