This game is so close to perfect that its few, minor flaws in conception really stick out:
Combos: The game is basically built around combos. But the combo count stops before the new tires fall from the preview onto the play field. So the game shows you the tiles that are next to fall, but it doesn't reward you for planning moves around tiles that haven't fallen yet.
When it gets hard: for the first part of the game, it is clearly going easy on you and only making new tiles fall where there is available space. But at a certain, seemingly arbitrary time, the game switches into hard mode and tiles start falling more randomly and faster. So it starts out seeming like the game wants you to succeed, and then abruptly it switches gears to make you fail. To me, this lacks grace.
Otherwise, like I said: perfect (as long as you have an ad blocker on your phone; if not, I wouldn't recommend it).