Things I like
I couldn't find a better way to submit this.*
While I did enter a short review via the iPhone app, I've been recording notes from time to time as I used Todoist. This was initially in response to an introductory email where Todoist invited me to tell them what I liked or why I was using Todoist (or similar wording). So here are some things I noted and like, followed by a handful of suggestions.
Very easy to learn and use -- intuitive and fast. One of the very best examples of programming I've seen.
You can click and drag a task to a different project.
The responsiveness (web page and iPhone app; also syncing appears to work smoothly,).
Backpack was going away (or at least they announced they weren't accepting new subscribers and I assume there wouldn't be many improvements).
Good support including a suggestion voting system.
The help pages are good and so are the keyboard shortcuts.
Good and easy searching.
It's a webapp.
Heirachies for projects.
Click gear icon and Move to another project.
Also like the "+" icon to add a task to any project (i.e. folders).
Some of these things I didn't realize before changing to Todoist. It is nearly perfect for me, yet on my first brief try I didn't realize enough to stay with it. The ~productivity stats orientation turned me off and perhaps made me think it was too complex.
Suggest adding "Copy to another project".
Assign a label to multiple tasks, all tasks in a project, assign to tasks and or projects based on a keyword (or even using regex or, probably better, all tasks found by a search query; can you search projects too?)
*(You should make it easier to find a contact email address to send something like this to. Or I should be smarter perhaps.)