hi
after playing the game for about 15 mins i have some suggestions for you.
first its a very nice game and i really like the graphics. i planned to make a similar game where a warrior is fighting through levels with his sword. there is a game that i really love that has the same concept and its one of the best games i played for android it is called "Sword of Xolan" and such game i am planning to do in the future.
anyway, back to your game:
1, first i want to say that level 1 is super hard. i didn't manage to finish it. it's TOO hard for the first level. you need to make it much simpler so people will not get frustrated and uninstall the game
2, there is an issue with the player movements. when you attack you cannot move and if you attack while jumping it looks like you reset the player velocity in the x axis. i am not sure if it is what you wanted to archive but i personally would like to attack and move while attacking.
3, when the player is on the elevator the jump is much smaller than on ground i also noticed small jumps while the elevator is going up (without clicking on the jump button, i guess its because of the speed of the elevator and the gravity setting of your box2d world) i had similar problems but i managed to solve them in my game "Pixel Knight", you may have a look
4, if you hold the jump button the players jumps in a loop when he touches again the ground. it remembers me of old childish games where the players jumps in a loop. i think its "bubble bubble" but i am not sure. i think it would be better to let the user hit the jump button again after he touches the ground. i have a variable where i store if the jump button was clicked and then i dont let the player jump again until he hits the ground.
5, you draw the player before you draw the whole level (walls, ground,..). and what you get is when you get close to the wall the shield of the player is hidden behind the wall and you dont see it i think it is more correct to draw the player after you draw the walls to avoid that.
6, when the player dies you should draw a different player state like lying on the ground but instead, there is a background with alpha where you can see the player still standing.
7, i really like the background music and the sound of the sword hitting the walls but you need more sound effects like jump or when you unlock the door. some nice animations like door going up would be cool.
8, i had a crash when i exit the game and then went back to it, i sent you a crash report.
9, you should catch the back key and ask the user if he wants to exit the game when he is in menu.
10, are you using native views for your buttons or only libgdx scene actors for your buttons?
bottom line i really like the assets and music and what you did. you are in a very good path and with some small improvements it can become an awesome fun game to play.
i hope you don't mind that i gave my feedback
best luck, ilan
ps: is the background you are using klaus avatar? (only pixelated)