well, as far as detail and lighting goes this very good news as it does look very good.
Halo: reaches battlefields are not going to measure in feet, they're going to measured in the acres range. as what Bungie has already confirmed in the Gameinformer magazine, halo: reach will sport a massive battlefield of 40 AI + 20 vehicles on screen. with very good character/weapon detail.
http://item.slide.com/r/1/147/i/6zqzajR84j91xMSbEgv6Nn_1bnlP-VTP/
http://item.slide.com/r/1/223/i/F1OxMC485T-_5jeMJK3_jWNl1OHxgLq_/
and very good vehicle geometry detail.
http://item.slide.com/r/1/75/i/EJuKfYeBsT9T9z4EXGnml0yJLksS_PD6/
Where Epic's gears of war2 has demonstrated it's Wars within a 300 to 400 foot radius, Bungie is going to be raising the stakes tenfold on that plus number of characters and objects on screen. (remember, we still haven't yet seen the FPS side of this project yet)