In short: you've done a decent Tetris incarnate there.
You ask for constructive criticism but it's kinda difficult considering it's "just" that - Tetris. The mechanics are solid, as well as the controls are. Can't help but wonder whether the in-game control buttons were designed for use with a smartphone/touchscreen device because if not I think they're pointless to have - tried it with a mouse and it just didn't work out. ;)
There's also a good amount of possible tiles, I've counted 13 (might be one or two off since I just can't count for whatever reason) which cover all the usual tetriminos along some 5-piece tiles as well as a single 3-piece one. This variety isn't new either but for people less eXperienced you could've maybe offered a "regular" game mode covering only the regular tetriminos and/or an eXtended preview window showcasing the neXt two or even three tiles instead of just one.
The effects (both sound and graphics) are well done and not overly distracting like in some other versions I've seen and played.
There's also a couple of badges, nothing too fancy but given the option it would've been nice had you turned them into NG medals, too.
The music bugs me somewhat, though. While that electro-esque theme befits the battery theme of your Tetris it's also annoyingly repetitive due to its shortness (to my ears at least). The bass line seems a tad flat as well. Additionally I personally feel that it doesn't match the pace of the actual game either. That, and it doesn't sound anything like the Tetris theme at all, which disappoints my retro-self... I grew up with the original Game Boy Tetris, after all.
Finally, on the 3 attempts I've taken I noticed that after some point (about half-way up the field) of stacking the batteries each time the game gave me no more "I"-tiles. Three times is a small sample with ~13 possible tiles to draw from but it felt strange...
Congrats on your impressive high-score by the way, how long did you take to reach it?