A Minecraft Veteran, I am an casual gamer & the creator of the DigiCraft Projects (in MC). I also run the "Best of Minecraft Awards," which run every year from December through January (exception: BoMA 2009 happened in February '10). You can sometimes see me on MC SMP at "The Voxel Box" server. I will also be doing "Internet Critic" videos starting late January 2010, where I will review things from the internet (of course). This naturally includes online games, such as Minecraft.
Game Review on Nov 16th, 2010 - 17 people agree 9 people don't
Minecraft is, in my opinion, the best Sandbox-Adventure Game currently in the gaming market. Though still in Alpha, Minecraft is able to combine the freeness of an infinite, open world to do what you please with a set of simple "life goals," namely: creating a successful mining/spelunking operation to obtain iron & diamond (the two most prized ores in Minecraft), kill monsters, bravely explore the Nether (Minecraft's "hell"), and make the most beautiful, stunning, impressive home you can imagine. Heck, you can even make a whole metropolis if you wish.
For those that don't know, there are 2 versions of Minecraft: Classic & Alpha. Classic is the free version (v0.30), and includes both a Survival Test Mode (which includes an early version of the current survival mode, as Survival Test turned into Indev, than Infdev, and finally, Alpha) and Creative Mode (where you have unlimited blocks, no monsters or health, and can just BUILD). Alpha currently only includes Survival Mode, which is the mode most see in the internet media, and which is the current, up-to-date version of Minecraft. Both Survival Alpha & Classic Creative have Multiplayer modes, so you can build and/or survive right along side your friends.
As Minecraft gets closer to Beta, and then completion, there will be even more things to do, more things to craft & build, more things to hunt & gather, and more fun to be had. Survival will become more difficult, putting more limits on you & making it slower, more focused on surviving (like the mode's name implies). Creative will be re-added & updated for Alpha (no one knows when, currently), and will allow to build what you wish without the limitations of Survival. Even more game modes are likely to be added in the future, too.
Minecraft's only limits are those of your imagination. If you have an open mind and a large imagination, you can create great things in Minecraft. So long as Creepers don't blow it up, of course.