Noted in a sibling comment, not being able to drag mail is a bummer. And on further exploration I definitely miss being able to search. But selecting it and moving it isn't too bad, and I can use mail.google.com when I need to -- overall I'm not concerned about a lack of features for this desktop client.

My guess would be that they applied the Aol user principle to the mail app and figured you'd use Outlook if you need a more featureful application.