I learned about Outerra and the Middle-earth project a few weeks ago and had it downloaded and was playing in it within the hour. When I first zoomed out into orbit I pulled a Neo "woah". I don't know what level of detail is possible in this engine but I'm eager to see Middle-earth fleshed out with all the locales.
A day or two ago I learned of another project called Massive Middle-earth that is being done in Minecraft. It's really cool that projects like these have emerged, and quite a neat coincidence that they've emerged at roughly the same time, with similar goals. I'll be playing around with both as they progress. Personally I think the minecraft version would be best for a pre-third age map (before Arda was curved) and this version would be better for the third age and beyond (although I'd love to see Beleriand, Numenor and Aman in this engine, to hell with lore).