I got Minecraft (Alpha) yesterday. I played for a few hours. I made a castle, a dungeon, and a house. I realized that's pretty much what the entire game was. It's like Legos, but slower and you can kill stuff. If you're thinking about getting it, the free version is almost exactly the same. The weapons/enemies don't really add anything to the game. Don't waste 9.95 Euros on it.
You are aware that Ver. 1.8 will have a mode where you have to eat food to survive? And an Exp system is being added too, I think.
That seems to me to be a big step in the right direction, getting back to MC's survival roots. They need to add a new enemy, one who can jump high so you have to build better defences, and have this new enemy have some good AI.
Notch is trying to appeal to everyone, and maybe that's the problem.