I hope no one minds if I chime in.
While there are some features I miss from Evernote 4, I agree with Kelly: you can implement a perfectly good GTD system in Evernote 5.
As an aside, I've set up my Evernote GTD system almost exactly as suggested in the Evernote for GTD guide published by the David Allen Co. I highly recommend it.
I've "deviated" from the guide in two ways. First, I tag the heck out of things. I understand the point made in the guide re: tagging -- if it becomes to burdensome you won't be motivated to maintain the system. But I have ADHD and have found that my mind is less "linear" than a lot of non-ADHD'ers. Adding multiple tags to many notes fits the way I think and has proven useful on multiple occasions.
Second, I forward actionable e-mails to Evernote using the Outlook plug-in and/or forwarding emails to Evernote. I find this to be a great way to process my emails.
Again, hope nobody minds me piping up. I realize this question was directed to Kelly and not to me.