The original Super Mario Galaxy was one of those titles that made many other games look amateur by comparison. It had beautiful graphics, grand music, and some truly stunning examples of difficult gameplay (the Luigi's Purple Coin challenge leaps to mind). The sequel, particularly the story, expects that you will be exceptionally familiar with this game.
So what's new in this game? You get to use new power-ups (such as Rock Mario or Cloud Mario), and one of the better things about the game is new (at least to the Galaxy titles) as well: the return of Yoshi. He comes with power-ups such as the Bulb Berry and the Dash Pepper. The Bulb Berry creates new pathways by illuminating spaces, although they aren't actually there when the berry runs out (as opposed to Indiana Jones and the Last Crusade, where the invisible bridge was all a forced perspective trick). For the most part, Yoshi's easy to control, but there are some difficult bits (for instance, if you're running up a slope with a Dash Pepper and hit something, you cannot regain your footing).
Sometimes, however, it feels as if the game doesn't know whether to mother you or leave you and assume that you'll know your way around. The version of the game that I got comes with a tutorial DVD intended to teach people who don't know about Galaxy how to play. The problem with this is that the tutorials aren't just confined to the disc (which I appreciate that not every copy came with); instead, there are hint televisions dotted throughout the earlier levels (and some later ones) to tell you how to get to certain areas, as well as a Cosmic Guide to take you through stars for you (although you do get left with a Bronze one and have to do the challenge yourself for the Gold Star). As if that wasn't enough, the characters that get dotted round the faceship (the spaceship hub area looks like Mario's head, hence 'faceship') tell you extremely simple things, like spinning and how to long jump. This can get frustrating after a while and save for the second disc are present no matter the package you buy.
However, once you get past the tutorials, the gameplay itself can offer some moments of joy. This is usually when you've just completed a difficult challenge for that elusive gold or green star, but sometimes in seeing how a particular level works or recovering from death in ludicrous ways.