As user [FOR]Mica aptly summarized, "Critical Mass can't decide if it wants to be frantic or strategic, and ends up being neither instead of both." If you go too long without making a combo, the block structure starts to rumble (go critical). You only have a few seconds then to make a combo, or only enough time to add a few blocks, but there's no timer or other useful indicator before the sudden explosion. There's also no indicator what the next block color will be, so you can't plan ahead much. If you were hoping to build up a bridge between two widely-spaced blocks for a big combo, well too bad, adding all those blocks in between could make the structure unstable. Even though planning for big combos is way more satisfying and yields a better score, it's like the game makes that awkward and instead pushes you for quick easy combos instead.
Worst of all IMO, the entire soundtrack is 8 measures that repeat over and over forever. It's a soothing trip-hop kind of beat, but ♥♥♥♥♥♥♥ it wouldn't have killed the developer to include an actual song or three. Even Tetris had multiple tracks!
So while the basic match-4 premise of the game and the graphical polish are great (even has a colorblind mode), some of the design decisions need more time in the oven.