Well, the visuals in the Reach beta were miles ahead of Halo 3 IMO. I'm not at all concerned about Reach's graphics. I'm more interested in the gameplay and story, which hopefully won't blow.
So where are the differences to HALO 3 in your opinion?
I remember that the weapon models looked rather good for instance, I could not check out the models of the enemies, as I typically killed them far away and we where constantly attacked.
The animations of the enemies did not look extraordinary as well, although some of the more advanced foes used kind of cool dodging maneuvers.
The map we played did not look special either with all the greenery and gras around. I did not had the feeling that the scope was extremely large, I had rather the opposite feeling: the enemies spawned (actually the got dropped of by ships) in a rather narrow area.
The one thing that I did not liked: it looked kind of rough. If I would not know that it is indeed nearly full HD, I would have believed that it was sub HD (for the record: the same feeling as Crysis 2 Xbox 360 and Black Ops Xbox 360 and Infamous 2). And sometimes the aliasing was really bad. I remember that this map had kind of steal/concrete roofs, and those edges flickered as hell. So, as aliasing was basically the only complain I had in HALO3, I am kind of dissapointed that they did not improve much in this department...although rocks and other stuff did not have this issue, some stuff flickered heavily.
PS: It is really sad that this game already got pirated. If I think about the MS booth, and all the effort they put in to let people test HALO:Reach, give hints, discussing stuff with you if you ask them, having lots of displays so that the waiting time is acceptable....and of corse all the money the invested builoding a new engine - booo to all pirates!