If you're completely unfamiliar with the PC version of Minecraft and want to know more about the game itself, you can find my review here. This port to the Xbox 360 doesn't deviate from that core gameplay, but there some key differences of which you need to be aware.
The biggest addition is the inclusion of couch co-op. Up to three friends can drop in to your world with a simple press of the start button. While Minecraft has always depended on isolation to a degree, the mood shifts when other players are added to the mix. The game supports typical online connectivity, but nothing quite matches putting the players in such proximity of sharing a screen. You don't even have to play cooperatively, you're free to attack each other or break down each other's constructions. You can thankfully set your world to exclusively invite only and hide your extra controllers if you'd prefer to keep anyone from messing with you online or offline. The only concern with having multiple players on a single screen is that it starts to become a tight fit; the option to switch between vertical or horizontal split is a nice touch, though.
Thankfully you won't need to struggle with the controls as much. I was initially wary at the thought mouse and keyboard controls being ported to a gamepad, but I actually found that Minecraft handled fairly well on the 360 controller. Movement still feels natural on the joysticks and a lot of interactions are mapped to the triggers. It's still just as easy to pull off little tricks like jumping in the air and placing a block below you or turning on the sneak/walking toggle to inch out on ledges and place blocks. The only time the controls becomes a bit of a bother is when you need to move several items around your inventory. The snapping feature helps but there is just no replacing a mouse for this kind of precise movement.
The new tutorial and crafting system are a welcome change. The tutorial will walk you through all the basics of mining, craft, construction and how to survive in Minecraft. Crafting is now done in a new window containing all the recipes to tab through. If you're familiar with how crafting works on the PC, the items will now be automatically arranged in the correct configuration, so if you simply have the stuff, you can make it. There are even tooltips for items in the world, giving you hints to which recipes they might fit. The net effect is that it makes the game much easier to jump into without resorting to outside resources like a wiki, but this comes at the expense of some of Minecraft's discovery. Taken as a whole, I think it's for the best. There's still plenty to explore in the world without needing to get frustrated over what exact configuration of milk, sugar, eggs and wheat makes a cake.
Lastly, you should be aware of what's currently not in this port. Survival is the only gameplay mode available. The game also currently runs an older version than what's on the PC (1.6.6 according to the wiki). Support for mods, texture packs and players skins are nowhere to be seen. However, stated plans are to add all of the functionality in future updates. So in some ways this mirrors how Minecraft was beta tested before its release on the PC.
It might also help to know that the Xbox 360 version works out to be a little cheaper, at least here in the US. 1600 Microsoft points is about $20 to the $27 on the PC. If you already have Minecraft on the PC, there probably isn't enough new stuff here - in fact much is missing - unless you're really enthralled by single screen co-op. If you're curious to see what the fuss is about and for whatever reason the 360 is your best or only method of playing, you're still getting the core Minecraft experience with this XBLA version. It will just take a little longer for some of the bells and whistles to arrive.