As many do, I quite enjoy sandbox-style games. I had my eye on Minecraft awhile back, but never really could give it a try until now. Currently, the site (and therefore the authentication server for clients) is sort of borked by all the traffic from Penny Arcade, due to their Minecraft comic series they started last Friday. You can get the game client from the skeleton site here. It won’t come with sound or music, but you can rectify that by following the instructions here. Once the site’s back online, the game will no longer be free to play, but you can buy the game for £10, and you get it and all future updates (for life).
Also, if you’re having trouble figuring out how to get started with crafting and surviving, then either check out the Minecraft wiki article on crafting here or watch this great series of videos on YouTube here.