One of the things I loved about Mercury was the mercury itself. It looked like mercury, which is still very impressive. This was one of the main reasons I wanted the original game. The fact that it looked real was critical for the games success, almost like you were balancing a blob of the stuff on your psp.
Mercury Meltdown should really be called Paint Meltdown, as thanks to cell-shading the blobs here look nothing like mercury. The game is garish, with even the menu screens relentlessly colourful. In essence the gameplay is the same as Mercury, perhaps even more varied, and so it can be worthwhile. It's just a pity the design lets it down.
Had the design been toned down a tad, and the mercury blob kept to its realistic look, this sequel would have been teriffic, and I would have chosen it over the original. As it is, the first one will always remain the more impressive game, and the better choice for adults looking for a puzzle on psp. Kids however, should prefer Meltdown, despite it being as challenging as Mercury. As an adult, if you play Meltdown, then play the original, you'll see why they shouldn't have changed it.