: On a side note, I'd be interested to see if the new visuals, or even the old
: visuals, "clean up" environments by having objects removed that
: are far from the player's area but still visible if you know where to look
: and are even reachable sometimes

If you're referring to not rendering things even when they're in the player's view, Halo's 1 and 2 are both pretty good about not doing that. That's not to say that there isn't lots of LOD; even Halo 1 uses extreme amounts of geometry LOD on dynamic objects. But most things that should be rendered, get rendered.

If you look carefully, you might notice that grass sprites in Halo 1 are only rendered in a small radius around the player, but that's the most obvious thing I can think of (and it's not that obvious). Objects also don't cast shadows when they're a long distance away, but you seriously have to be looking for that. Halo 2 is mostly similar in this respect.