I agree, I also bought/gained knowledge of "Threes" after first playing 2048...
To add to the differences in game play you listed, I find myself managing the pairing of RED and BLUE tiles in "Threes" more of an objective than matching the numbers because if you don't the game quickly ends.
To add to the differences in game play you listed, I find myself managing the pairing of RED and BLUE tiles in "Threes" more of an objective than matching the numbers because if you don't the game quickly ends.