Simple, which is good, but...

2015-08-26 update: I like the app. I want to like the team. However, theyve routinely turned down iCloud requests. Even when the work was offered to them free of charge. This makes using this app an exercise in "when will I lose my data," which isnt a game I like playing. -2 stars for failing to even acknowledge multiple requests and, later, offers of free work.
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With one glaring oversight: you cannot go back in time and edit blank/missed days. Fix this, and the app will be brilliant as a quick mood-tracking app. [Update: you can now go back one day. Serviceable.]

And iCloud support. I recently got a new phone and nearly lost a years worth of tracking! iCloud, man, put the SQLite file in iCloud! :)

ChrisP_77 about Mr Mood