The first Super Mario Galaxy was generally thought of as an amazing game, and was well received by most people. It hearkened back to the goodness of Super Mario 64, and made us almost forget about Super Mario Sunshine. Super Mario Galaxy was superb, as a single player experience, but the less than perfect co-op was disappointing. Player 2's options were seriously limited: shooting star bits, holding enemies, and assisting Mario's jump. While this was great for casual fans, particularly young players, more experienced Mario players wanted more. Super Mario Galaxy 2 has delivered improvements in this respect, though the co-op is still not ideal.
Player 2 has a few new tricks up his or her sleeve, and each of them are extremely useful. Most obvious is the inclusion of an in-game character representing the player. In Super Mario Galaxy 2, the second player is an orange star person, floating along with Mario through his adventure, no longer a nameless star reticule. I know it sounds superfluous, but having an actual avatar of sorts in the game adds greatly to the co-op experience; it feels more like you are a team, instead of just an afterthought. This star person is appropriately named Luma, and has all the same star-shooting and enemy-holding abilities of player 2 in the first Super Mario Galaxy.
One new ability for Luma is collecting coins and other power ups. By holding the star reticule over an item and pressing A, Luma shoots out, grabs the object, and returns it to Mario. This makes collecting 1UPs, coins, and other valuable items far easier. In many cases, Luma is able to easily reach things that Mario would be hard-pressed to get to alone. You'll feel as is Mario couldn't do it without you, and that's sorely needed in a game where Mario is clearly the star (pun intended) of the show.
Luma's interactions go a step further when dealing with enemies. Zipping out at the press of the A button, Luna holds enemies still, allowing Mario to avoid being overwhelmed. Best of all, some enemies can be dispatched by Luma alone! A few vigorous shakes of the controller, and poof, bye bye bad guy! There are a few caveats: certain enemies can't be wrestled into submission by Luma (Bullet Bill, for example), and most bosses can't be held at all. Still, this new ability is extremely useful, especially when the action gets frenetic, as it so often does in Super Mario Galaxy 2.
As for the rest of the game, it is, quite simply, the greatest 3D Mario experience ever. Indeed, I would go so far as to say the level designs are the most clever and innovative I've seen in any game. The first Super Mario Galaxy had some great levels, don't get me wrong, but with the sequel, it's as if the developers truly realized the potential of the premise of "Mario in Space". The new power-ups, like the Drill, Cloud Flower, and Rock Mushroom, are well implemented. The Drill is my favorite of the new abilities, allowing Mario to tunnel through soft earth at breakneck speed, switching between the surfaces of worlds in a dizzying snap.
Yoshi is back, as well, and even the friendly dinosaur has new abilities, like turning into a blimp, and lighting up invisible platforms. Yoshi's trademark "gobble and spit" move is used at length, and his tongue can also be used to swing off certain objects. Luigi is available early on as a playable character, and beating levels as Luigi opens up time challenges, adding longterm appeal for the hardcore platform game champs.
The first Super Mario Galaxy was a good fit for casual gamers, and this casual friendliness is even greater in the sequel. TV screens found throughout the levels give tips and tricks, some even showing players how to get past particularly tricky sections. The "play it for you" feature from New Super Mario Bros. Wii returns, too. Adding to the casual appeal, the map navigation system is more like that of Super Mario World than the pretty but confusing style of the first title.
Super Mario Galaxy 2 is one of the best gaming experiences you'll ever have. A constant parade of jaw-dropping moments combine to set the new standard for 3D platformers. It is a marvelous game, so good that even Player 2's limits don't really detract from your enjoyment of it. But the co-op doesn't hold up to the extremely high standards of the rest of the game. Playing as Luma isn't the same as using Mario, and I cannot give a game with co-op like that of Super Mario Galaxy 2 a high co-op score. It's by far the best and most polished "B.Y.O.B." co-op out there, but it's still far from ideal. In all other areas, though, Super Mario Galaxy 2 is the pinnacle of platforming perfection.