What type of methodology to use for unmoderated testing?

A colleague of mine would like to get some feedback on a new interface that we've already launched. The feedback would be given by 5-10 users, remotely, and unmoderated - we'd give them the interface and then ask them to complete some sort of feedback on their own, in their own environments.

What approach should we take? A questionnaire? A few tasks followed by a satisfaction scale? I've tried to get my colleague to lock down the goals of her testing, but I think it's generally to see if the platform can accomplish what it's supposed to accomplish and whether there are any pain points for users (including look and feel).