The primary goal of the game is to match up coloured blocks into groups of four or more before they fill up the box, similar to Puyo Puyo, except the blocks actually "tumble" down when positioned vertically, akin to a Slinky; as the player acquires a specific amount of points, the game moves up a level.
Initially, the game begins with only blue, green and red blocks. As the player progresses up the levels, however, the game slightly increases the falling speed of new blocks, as well as including more block colors:
- Yellow blocks are introduced from level 5 onwards;
- Purple blocks are introduced from level 10 onwards; and
- Orange blocks are introduced from level 15 onwards.
To counter the increasing difficulty of the game, the player is given the option of acquiring special abilities by stacking 4 blocks of the same color to form the shape of a square-shaped grouping (2 blocks by 2 blocks); note such groups will not remove any neighboring blocks of the same color. By stacking four such groups, the "Power" bar will be filled, granting the player the ability to choose one of four "Special" tricks that aid gameplay. Each "Special" is marked by a different color and is triggered by a specific command:
- The red "Special" removes the lowest four rows of blocks.
- The green "Special" removes the middle two columns of blocks.
- The blue "Special" allows the player to remove all blocks of any selected color in the box. The player must press the same button or key that activated this ability again to select a color.
- The yellow "Special" momentarily stops the any new blocks from falling on its own, allowing the player to control its descent on their own accord.
A minor drawback to this feature is that the player can only hold a maximum of 3 choices of special abilities at a time.
This game can be played at many locations throughout Liberty City, including:
- Homebrew Cafe, Broker.
- A back room in Perestroika, Broker.
- Modo clothing store, Algonquin.
- The Triangle Club, Northern Gardens, Bohan.
- The Lost MC Clubhouse (only in The Lost and Damned).
- QUB3D shamelessly declares itself "THE PUZZLE GAME YOU'VE PLAYED BEFORE" in its main menu, alluding to the fact that puzzle games of the visual matching variety are all very similar. Another reason why it says this is because it is very addicting and you might end up playing it a lot.
- There is a QUB3D machine in the St. Mary's Community Project in Bohan but the player cannot access the machine since the interior is only visible during cutscenes.
- During Mafiya Work in GTA IV multiplayer, the player may be tasked to destroy QUB3D arcade cabinets.
- The game itself appears to be based on classic arcade game Tetris.
- If you open the High Scores table, you can see some unusual names such as "TIT", "ASS" and "COK".
- In GTA V, some QUB3D machines can be found throughout the world, but cannot be used.
- One of the initials on the high scores scoring 10900 is LIJ, which would be the initials for Little Jacob. This is very likely because the Homebrew Café is one of his favorite hangouts.
- You can hear the song of the game when passing in front of Videogeddon.
- The whole game is in the sky, Liberty City can be seen on bigger render distances, and some video cards that make fog weird. That means a player can take them with mods to spawn props. The cubes itself appears to have the size of a standard vehicle's wheel.