I haven't downloaded the Outerra demo yet to have a lash: just too busy, plus they are still having issues with their graphics driver working with modern AMD HD-series video cards (like mine). But the videos (in hi def) that I've seen posted are excellent (given the Alpha state of Outerra). In fact even in Alpha, the atmospherics & sea boundaries are still quite away ahead of most simulators I've seen (whether they be flight or otherwise). The dusk and dawn of Outerra are particularly good: no stars appearing where they shouldn't and such. Indeed, one of the videos I saw of a very late twilight was very realistic. And since everything is rendered procedurally, one doesn't get that awful pixelation up close like on FSX - that alone is a huge step forward in simulation. I don't know HOW close one can get before some pixelation occurs, but "standing" on the beach or in the grass and viewing the scenery looks pretty detailed and un-pixelated. The recent addition of moving grass (in the wind, Ian, not by itself...

) is a nice effect too.
It's safe to say that Outerra is a very long "work in progress", which I find exceptionally frustrating. The team of guys working on Outerra is very small, and it sounds like none of them are full-time on the project. They seriously need a financial backer: if I had the dosh, I certainly would, as I can see the depth of the work they are putting into the fundamentals.
It's fair to say that anyone wanting to have a go at creating a complete earth-like simulation framework has really got their work cut out for them, seeing as how even simulating the major "basic" mechanisms of planet earth is a major undertaking. Reading the post that Kelvin linked to and others (since I keep an eye on development and check the site every 4 weeks or so to see what's new), it's clear that they are carefully thinking through the "basics" like landclass rendering (since theirs will be done fractally, unlike like FSX), rivers / lakes & general water types, vegetation and "weather" (which of course encompasses things like clouds, rain, snow etc).
I've often hankered for a simulation engine that will at least bring "deformable" terrain into play, especially for battle situations (but would be good also if one manages to crash in an aircraft - be interesting to have the objects interact with each other as they would in real life, to a degree). It might be nice to be able to sit behind a brick wall and be impervious to tank or rocket fire as the sim can't "deform" the wall, but it's far from realistic. And when the shoe's on the other foot, it's damn annoying!
Perhaps what's really needed is for a group of simulation programmer geek-types to get together with the guys from Outerra, plan out whose going to work on what, then parcel it out so that the work can be completed more quickly. Then once the component code for each of the "modules" is complete, they can be pulled together and integrated. Still a h*ll of a big job, but "more hands make light work".