So I've been a huge pureMVC advocate for quite some time. It's been great on large projects and scales well. It is also very well tuned for large group development.
One large issue I have had with pureMVC in a word.. boiler plate code.. ok that was 3 words.
At any rate.. it took a while to set up a project and get it off and running. Adding new sections could also take a minute to setup. But once it was setup it worked like a champ.
Robotlegs brings the goodness of pureMVC but seriously simplifies on the setup. Albeit it still has a prescribed way of setting things up for organizations sake.. it tries to stay out of your way. Also, dependency injection is a breath of fresh air to be sure.
Coming from pureMVC it was a snap to acclimate myself to robotlegs. Coming form say.. swiz may not be quite as amicable.
If you're interested in finding out more do check it out at robotlegs.org