What do you like best?
Formidable's purpose is simple enough - easy design interface, controls in plain English, and even some advanced filters to get you along. As a plugin that you can use to create frontends to SQL databases, and an entire universe of PHP customization, make this a truly Formidable plugin.
What do you dislike?
Views are easy to make, but a little difficult to make pretty. If you know basic HTML, then doing a table with some rows is easy enough, and the output looks as expected. There is another plugin called wpDataTables that makes the marriage complete! Easily add super powerful data display and editing capabilities to front-end users with a few clicks.
Recommendations to others considering the product:
It seems like you can take a dive off the deep end, but really it is like any other programming language - you learn the parts you need and ask for help on the parts you don't understand. Formidable's support is top notch and I've never received support like that from ANY product I've used.
What problems are you solving with the product? What benefits have you realized?
As a plugin that can handle CRUD Create/Read/Update/Delete - I have found it indispensable as a tool to create complete modules for specific tasks within a company, and I can tie all that information back together for reporting using SQL.