1 - I'm always getting stuck on a map edge. Being this by activating the primordial beast near something and as it's area is bigger than the normal char it will get stuck and then I will need to exit the game losing all my invested money and affinity. This is a big problem when you are starting to level up because you are poor or when this happens 5 times in a row and you can't complete the 3 maps for the "next level" is "not awesome".
2 - Being able to sell items on not absurd slowly pace.
Need to wait almost 1 sec to sell an item really?
3 - Can't use key binds to make the bad movement not so bad.
When you use a skill and then click on the ground to move, if you do this somehow fast, the character wont move. It's like when you click on an item and you attack the mob that it's not even there. So, there are 2 possibilities to easily improve this. The first one is to let the player force move on a "good key" this being for example the mouse button or using the wheel up and down (not just 1 of them), OR you can remove the bug itself.
4 - Items are always vanishing and changing order on the screen. For example when I'm trying to click on a yellow and it vanishes and I instantly click on a useless white.
5 - (Not so important but still) When you reach the champion difficulty it is not obvious that you can run it without any level selected. This means new players (in most cases) will lose at least 2 hours making every single test but to do run it with no difficulty.
6 - Lag when a lot of monsters are on the screen and you kill them all at the same time is a think and you can even get disconnected from the server. This is the one of the biggest issues that players quited playing Diablo3.
7 - The graphics are amazing and the base of the game is pretty good but this game has a lot of time and there are a lot of things that makes us players think that you don't care and you didn't even tested some simple things on the game so please, make them wrong ;).