As others have said, it really is a good value. It's cheap enough that I don't feel bad playing it in phases. I'll get all into it for a while, then something (like this time, Neverwinter) will take up my time, then eventually I'll be back to building. It's one of those games that you can just "play when you feel like it" and feel like you got your money's worth. It can be terribly addicting.
Edit: and you can totally get into it if you wern't there for initial ground-breaking. The world is huge, and you can easily run off to your own area of it and play around with a fresh landscape.
The wiki is fairly up to date, and a good place to start learning what you can build: http://www.minecraftwiki.net/wiki/Crafting#Basic_recipes
What version is your server currently on? Any Mods?