Mercury Meltdown is the sequel to Archer Maclean's Mercury, a puzzle game where your job is to guide a blob of mercury, or several blobs, along various mazes by tilting the game world, while hazards try to zap, attract, repulse, eat, or blow you up.

Mercury Meltdown features a new vibrant visual style, a lot of completely new stages, a free-look camera, ghost mercuries and replays for your best times that can be saved, and much more. The game's original realistic graphics have been turned into a more cartoon style. The mercury now has a black line around the outside of it.

The main change in the game is the ability to change the mercury into 3 more states. Besides the normal state, now you can turn the mercury into the "Fast" or "Slow" using a heater and a cooler, and using a solidifier, you can make it unto the "Solid" state, a round, non-breakable ball. The mercury can still be split using a splitter, needed to solve certain puzzles.

Unlike the original Mercury, the game is split into themed "Labs" rather than “Worlds”. There are 10 Labs, with 16 initial stages: Astro, Bio, Chemical, Electro, Geo, Atom, Aero, Hydro, Micro, V.R. (Virtual Reality). The PS2 version adds two more: Chrono and Cryo, as well as twin analog control, support for the rumble feature, improved graphics, and all the levels from the original Archer Maclean's Mercury. There are 168 stages in the PSP version and over 200 in the PS2 game. Unlike the previous game, there is no strict order to play the levels. Once a Lab has been unlocked, you can play all the stages included right away.

Attributes show how well you do in the games. The best performance is awarded with a golden cork, based on four conditions: a high score (a 1 sticker), all bonus items found (a star sticker), 100% mercury (a corked test-tube), and complete the level within the time limit. While playing, your progress is measured in faces that replace the time clock. The time limit cannot cause the game to end anymore; instead, it just turns into a sad face, and players can still complete the level. The mercury limits have also been removed, but 100% mercury is still needed to access some of the later stages.

The top right corner shows a color chart to help with mixing colors in the game. This can also be done in the paint shop. This release adds multi-paintshops, triangle base pyramid-shaped constructions with 3 different colored gates on either side.

In addition to the main game, there are now five party games, which are unlocked by collecting the bonus stars in the main game:

• Metrix: puzzle games where colored blocks need to be fit inside a pre-defined grid.
• Paint: move the mercury to paint the tray as much as possible against your opponent.
• Race: guide the mercury around the speedy track with boost pads and avoid falling off.
• Rodeo: tilt the playing area to keep the mercury on the field, while a fan tries to knock you off.
• Shove: aim the mercury at the center spot of the target, just like curling.

All the party games can be played in multiplayer over Wi-Fi on the PSP. The tutorial is now separate from the main game, and there is an additional Playground mode where you can test the different items in the game.