Minecraft
If there is a single redeeming thing about Java, it's Minecraft.
There are a lot of things that Minecraft tries to do, and it doesn't succeed at a lot of them. Of course it's in "alpha" right now so that's hardly surprising. What is surprising is how awesome it can be when it's at its best. Specifically, in the "mine" part, and in the "craft" part.
Mining isn't like in World of Warcraft where you wander around looking for mineral deposits: in Minecraft, the world is your mineral deposit. Make some torches and picks and shovels, dig a staircase down, and see how many gems and ores you can find before reaching the bottom of the game. The randomly generated map is full of surprises, and they're always fun to explore (except the ones that fall out of the map).
As for crafting, there is an item-crafting system (which is how you get the aforementioned torches, picks, and shovels) but that's not what I mean -- that system could use some work, I think, since the crafting materials are impossible to know unless you just google it. No, the crafting I like is more like LEGO. Whatever you dig up, you can use as a building material. Hence, castle. The more advanced stuff is pretty well beyond what I want to put into a game, but, come on. Castle! Awesome.
There are a lot of rough spots around the mining and crafting, like navigating the huge map, which I'm sure will be addressed as the game's development continues. What worries me most is the combat, which is kind of shitty right now, since to make a bow (the only projectile weapon) you need to get string, from killing giant spiders. But you have to kill them without a bow. Meanwhile, skeletons are firing their bows at you. Dicks.
But combat is entirely avoidable once you lay out your network of underground tunnels, and craft some doors. Awesome.
Progress: Gave Up -- Mined the earth, built a beach castle