Groovy / Grails. It's what we chose to base all of our products on and it has worked out really well for us. If there's any complaint / negative, it might be that the ecosystem is in a bit of a "state of flux" with Pivotal dropping support for Groovy and the language moving to the ASF, etc. One bit of fallout from that, for example, is that the GGIDE isn't available for Eclipse Mars yet (or it wasn't last time I looked).
Still, it works, it's easy to learn, there's a rich assortment of plugins for adding functionality, GSP's are nice, it's easy to make custom taglibs, etc., etc.
I'm hoping v3 support turns a corner soon - IntelliJ 15 public preview now supports Grails 3. I'm thinking this may get more people back in to it, and more contributions back. It's been in a limbo state since April, and seeing jetbrains support it (finally) gives me more reason to continue to support it.
I would have agreed till Grails 3. It doesn't work in so many different ways and it's never clear why. The reload stuff seems completely broken if you have dependencies that use many Java 8 features.
Still, it works, it's easy to learn, there's a rich assortment of plugins for adding functionality, GSP's are nice, it's easy to make custom taglibs, etc., etc.