We went in October and had a great time. For us, the highlights were the Nightmare Before Christmas Sing and Scream with Jack and Sally meet (though, they maybe need to redo that meet as a ticketed event or something because we waited a LONG time), the adult costume contest, getting to see all the characters in costume as well as all the other guests amazing costumes, and our Facebook group stateroom trick or treat. (The last being not an official activity but something we organized on our Facebook group.)
We had so much fun, but we are huge Halloween fans. I felt like the balance was perfect between regular cruise stuff and Halloween cruise activities. It didn't beat you over the head if you weren't into it, but if you were, it was easy and fun to participate. My full trip report is linked from my signature if you're interested in reading all about it.