Minecraft.
(Here is a video from me making a timelaps)
http://www.youtube.com/watch?v=xFVejoUDTAQ
I know this game is far from perfect. Optimisation problem and using Java for a massif game like this... But for most of the computers, the performances are okay, I can make an infinite world, the community is huge, MCedit is realy nice to create, copy and paste chunks and bits of maps.
But, The game have his limitation. Going vanilla (No mods) make the game a bit repetitive, not enough materia to create a lot of style. And, the fog distance is a bit small, it's hard to make an epic view of a large work without an external software.
There is other games that look like minecraft that could be interesting too.
Blockscape, an Alpha game that is slowly showing potencial.
(oups... during this bit, i went to check what was the language the game was written in... C# using XNA platform and XNA has stop any developpement... u-u)
Spoiler
But... The game is still in alpha and is too early in his developpement to be stable. It can crash a lot for no reason. And even without the crash problems, The controles are not that good. The caracter is slow and can easely clip and stuck himself (due to some polygones placed wrong by the procedural generated terrain) and the interface need work.
I though of maybe mapping for Hafl-life 2, but the maps are too heavy and it's a bit hard to share that kind of thing, due to the massives ressources it needs to work.
So... yeah. I'm asking to myself, should i continue with minecraft, of go for another game with another engine to try something different, have better result visualy and continue to be as easy to share the things i do.