My single biggest complaint is how incomplete the support for music from Bluetooth is. It doesn't show progress of music playing from the phone, something that 5 year old cars do well. It doesn't have a way to make the phone a favorite, so you have to go through multiple screens to switch to your phone for music.
This is very easy for Tesla to fix. I hope they do so soon.
Road noise from the wheel wells could have been dampened better. Although it does help to differentiate a 3 from an S/X, it is an area where 3 does not compare well to say a BMW 3 series, IMO. This is the sole feature of my 3 where I'm like "aw, man."
What I dislike most about my Model 3 is that I haven't gotten it yet!
On a more serious note, I dislike the fact that there is no keyfob. I can live without a HUD, CD player, physical buttons, etc.
But I hate not having a fob but having to make do with those stupid keycards or using my phone as a key. That's the only thing I really, really dislike about the Model 3 in general.
The #$%^&*()_ phone as a key. Great idea if it worked 100% of the time. Sometimes it will unlock the car and then demand the key card to drive 10 seconds later. Sometimes it won''t unlock the car and you have to try random things like restarting the app or phone or Bluetooth. Fob should be an option.