I knwo this sounds odd, but a lot of people on the Google Play area that does 1 star remarks are usually because of either UI or the touch feature. 

So this is my 2 cents on it. It's mainly on the touch controls.

Button Feedback

1. This lack of feedback sometimes can be a bit annoying and can even be a turn-off for some people because they wouldn't understand whether or not what they want to do is actually happening. 

ex. Doors - it takes a while before it tells you it doesn't open. Perhaps a tutorial when you first see the door or something? 
Even a "tutorial" level? and probably give an option to skip it for advanced players. 

2. Equipping Items

I wasn't even aware of how to even equip items before I double tapped it. 
I know a rating said they tried to "use" it, which obviously doesn't work. 

3. Dragging Potions 

What I mean is when you look at your inventory and drag one of your potions to your hotbar. 
I feel that when you try to drag it, it scrolls to the left and right, or it doesn't do anything. 
Half the time I try to put it on my hotbar, but it seems to drop the potion or even use it.

4. Targeting 

I was not aware of this feature. And this seems quite important since some monsters you want to take before others. Probably this can be noted in a tutorial as well.

I may expand on this as I keep playing, but overall this is a great game! I am very happy with the purchase and it's well worth the dollar that I spent. =)

Development is now going to focus on adding interface enhancements, gameplay enhancements, and a couple tutorial features.

1. I need to change several buttons to change state on touch down and then activate on touch up.

2. For equipable items, I should have a button for equipping.  Double tap is handy, but people who are new to the game would likely prefer buttons that tell them what can be done with items.

3. You can double tap to equip potions.  The drag and drop can likely be improved, but I'll have to play around with it a bit.

4. I'll need to cover targeting in a tutorial.

What I will likely do for the tutorial is extend the starting level.  The player will be able to take one of two paths.  One path just ends up at the starting location.  The other path will take them through some tutorial segments.