I'm not going into details about how good this player sounds. There are plenty of reviews that will explain it better than I would.
So let's get to the bad stuff.

1. The UI is straight up unusable. I didn't make this video, but it illustrates my experience/frustration with it perfectly:
2. There is a gapless playback switch, but it doesn't work. All it does is make the gaps shorter. I'm not joking. Look it up if you don't believe me.
   
3. This may not be an issue if you don't use IEMs. But with sensitive IEMs, there's a very noticeable background hiss. Comparing to some of the other players I've owned/tried, the background noise of AK Jr is significantly louder than Walkman A35 and FiiO X5 2nd gen.
4. The USB DAP function doesn't work. Well, too much has already been said about this one.
5. This may be the worst part. This player seems to have been abandoned by AK. The latest firmware for this player was released in 2015. There are PLENTY of things that should have been fixed, but they never did. Like lots of other people, I've lost hope at this point. If this is how AK treats its customers, I don't know if I'll buy anything from them ever again.