In fact, the "big breakage" in Scala everyone loves to cite was the addition of better collections. Just like C# did in 2.0 and now finally drops the old non-generic ones with WinRT/Metro.
The reason it gets so much flack is that Java developers want _binary compatibility_, because that's what they are accustomed to and Scala gets often used by Java developers.
Java developers would target the same criticism towards C# if it would run on the JVM.
I take the part on Scala back.