Rotation isn't very responsive on touchscreen. Also, it'd work better if it were played on a 13x26 grid. Not to mention that Pentris has to be played proactively rather than reactively, so a hold system and a five piece preview are basically a must.
Also, completely random pieces far mi ore often than not lead to dead board states, so you should really implement an 18-bag randomizer containing one of every single sided pentomino (all 12 free pentominoes + the 6 pentominoes that complete chiral pairs)
Not to mention that the dev of Pent-Up (formerly Pentris Plus) ended up establishing a very logically sound color scheme that groups pentominoes into families based on observed usage in gameplay, and this color scheme has become a bit of a de facto community standard of sorts
Here's the color scheme:
The exact hexes of this color scheme are as follows:
Top row: #00FFFF, #E52521, #59B343, #EF7921, #F7D308, #EF7921, #214194, #E52521, #59B343
Bottom row: #AF298A, #F7D308, #F7D308, #F7D308, #F7D308, #AF298A, #AF298A, #E52521, #59B343