Day 1 of ownership on my 2016.5 GT AWD and the things I do not like are:
1) Chrome vents are horribly reflective to the point where they actually obstruct the image in the sideview mirror. They look lovely, but this is just silly and such blatantly poor design it's kind of amazing no one at Mazda thought it was a problem. It's almost a safety hazard. I am going to figure out a solution ASAP.
2) Center console wiggles. I thought it wasn't properly attached but the dealer showed me another one and it wiggled just as much. It feels cheap and makes me concerned about how fragile it may be.
3) The Bose soundsystem is totally unbalanced. It sounds pretty good, but you have to set the fader pretty much all the way to the rear or it sounds like the music is coming from right in front of your face, and the EQ is just weird - very mid heavy, but also kind of processed in a way that emphasizes parts of music in a very unnatural way. It's one of the more bizarre default sound systems I've encountered and I'm surprised it's considered not just acceptable by Mazda but their upgraded system. It's not a high priority right now but I'm going to have to do something about it eventually.
4) Glove box is absurdly tiny and has no lock. Not a huge issue but it's the smallest glovebox I've ever seen and it's on the largest vehicle I've ever owned, it just feels wrong to me.