Well, ofcourse it's worth it. I've bought minecraft two years ago, and I never really been bored of it. Maybe there's months where I stop playing for a while, but I get right back into it, which doesn't happen to me a lot since I get bored of games quickly. Minecraft is a game that could be highly modded, sort've like GMOD but way different. It's fun since you could make buildings, survive with friends (VERY FUN), and just screw around and blow up cities with TNT.tl;dr It's an awesome game that you don't get bored of, worth the 30 bucks. GET IT!
Multiplayer is really where it's at. If you find a decent community, you can spend hours of fun messing around and working on projects with friends. I found singleplayer getting really lonely after a few sessions.