Good idea, the powerup were not present enough to really feel like it was an interely different game than tetris. Maybe it could be improved with having the powerup mechanic apply more often to be more of a contraint
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When initially coming up with the concept, we thought that the power-ups would be more useful than a hindrance, so we made them a reward for clearing lines. Your idea of using them as a constraint or stage hazard would be really interesting though, and I'd like to see how that changes the overall strategy.