I have used Scala for building business solutions since 2012. I had been maintaining PHP and Rails systems of 50k to 150k LOC prior to the switch. I still have to maintain PHP and Rails systems. The move to Scala was driven by the need for better performance, system resiliency, and to mitigate the effect of multiple developers coming in & out of a codebase. It turns out to be ideal for this.

Idiomatic Scala is not a grab bag of features or paradigms. It is firmly based on programming with expressions and using the type system to improve abstraction. Statements and mutable data structures show up when interfacing with external systems or for performance reasons. The Collections libraries are arguably "object-oriented" as that term is commonly understood, but this is not typical for application code. However, object-oriented features such as objects, classes, and traits are the basis of Scala's module capabilities.

For programmers coming from 20th century mainstream languages that are all based on programming with statements, mutable variables, and are arguably a thin abstraction over the machine itself, programming with Scala can be a challenge. If you want to do your familiar imperative style of programming, Scala is going to be painful. Use another language. But if you would benefit from a type system and good support for expressions, then Scala is possibly the best choice currently for growing business applications. We are not in 2005 any more.

Scala is not ideal as an introduction to functional programming. Other languages, such as F#, SML, OCaml, and Haskell have better, simpler syntactic support for features associated with functional programming.

People who dislike on Scala are probably either stuck in the past or don't have pain that Scala would solve.