We have a Milestone 2 build of MPS 2.5 ready for you to test and experiment with. It received a massive amount of bug-fixing and polishing and should give you very realistic experience of what is coming in 2.5. Get it fresh from from 2.5 EAP download page.
If you want to refresh your memory about what new functionality 2.5 provides, a list of the new features is to be found here.
Enjoy the ride!
Develop with pleasure!
-JetBrains MPS Team