Remember that game you used to play as a kid that involved you moving a small ball baring through a wooden maze without letting it fall down through any of the holes? Well think of that, but intensified and that's probably the best way to describe Mercury Meltdown from Ignition.
The second in the series, the game once again lets you take control of a liquid Mercury "blob" and then spend the next 160 levels avoiding various obstacles and hazards to reach the end goal.
To spruce things up a bit, the Mercury blob itself has now been given an overhaul and has four varying "states" Normal, Solid, Fast and Slow. These states add an extra dimension to the game play and according to Ignition allow for large complex levels than seen in the previous outing.
The extra level of toughness is that, as you might have guessed, Mercury isn't exactly a solid so how much you scrape the sides of the walls will decide how much your ball stays in one piece.
As with all puzzle games, the levels themselves start off fairly easy with a nice learning curve and plenty of chance to earn bonuses along the way.
This isn't going to be the biggest must have game of the year, but it is a nice aside to keep you from getting bored on the train. Like the original Victorian game you used to play as a kid, you'll either find this the most addictive or frustrating game on your PSP. Bearing this in mind if you can get a quick play before you buy then you'll know which camp you fall into as there is no middle ground here.