Halo 4 does look better than Reach overall but so do many other games. The biggest improvement I see here is the lighting, other than that it's more or less the same as Reach with pros and cons. My biggest issue with the Halo engine is the lack of environment details, I still see low poly geometry, barren landscape, less than stellar texture res and an overall sterile look compared to games like Killzone, Gears and Uncharted. But yeah, one can argue a more openness playing field vs more linear approach.