[state_machine]

As someone who has used Lift in production on a non-trivial webapp for the last 18 months, and has used Play 1 and 2 in both Java and Scala for side projects, I would not recommend Lift.

The "the-view-is-the-controller" approach encourages a messy blend of logic and presentation, with lots of HTML ending up in your Scala code.

It's stateful in the extreme, using opaque callback identifiers to identify serialized closures, so rather than having a nice, clean, easy to reason about boundry between your app and the outside world (your routes file, controller methods, whatever), any code anywhere could be invoked by someone clicking something in their browser.

Validation now needs to be enforced in the models, since you no longer have a single place to check it as it comes in. It goes beyond that and embeds rendering logic in models, which have to toForm method which generates HTML.

The extreme statefulness also means you lose everything when you roll a server, you need sticky sessions, you spend way too much time GC'ing and you need far more RAM/user.