I mean this fantasy theme he went with. He added a dragon, castles, fortresses, and quest givers, but he never really completed the idea. The quest givers don't give quests, the dragon is a boring fight that is longer than it should be, and the fortresses are pretty much empty. If he wanted a fantasy theme, he should've stuck with it and went all out with it. Right now, it just seems unpolished.10/10, in the gaming world, does not mean a perfect game. In most art mediums, 10/10 doesn't mean perfect. As for your complaints about more features in a sandbox game, well, I guess Notch should just stop adding things to the game? Right? And I don't even know what the "theme" of Minecraft is, unless you're talking about the theme of building stuff.
Also, to what you said in the post above: He can still update it, plenty of games update their games regularly with new content. It's not an excuse to release an incomplete game, though.