Recently on Bungie.net int he Bungie Weekly Update, they confirmed that Halo: Reach is indeed using a brand new engine.  With that also came some information that the trailer we all saw was really not running real-time technically speaking,

The Halo: Reach trailer was produced directly in our new game engine using real game assets. Because the game is still in the midst of development, which means things like framerate are still in flux, we do something called a “frame dump” that lets us spit out the content, frame by frame, and then compile it back as the video you all saw on Saturday. We can actually run this same cinematic right now, within the latest game build, but it’s not always at the consistent smooth framerate of the final game (yet)

Well, that’s as close to real time as you can get.  I’m sure the actual product will look and run no different.  Bungie then went on to say that trailer represents the “visual bar” for the final game and that the trailer and actual game should be “near identical” next fall.

This trailer absolutely represents our visual bar for the final game and is near identical to what you’ll see next Fall. The single biggest difference between this trailer and the final game will be the extra generous amount of anti-aliasing (the smoothing of “jaggies” or edges of pixels) present in what you’re watching right now but rest assured that Reach will be significantly improved in this department compared to Halo 3. (The extreme “AA” in the trailer was due to the “frame dump” mentioned above.)

So they gave it a little more “AA”(anti-aliasing).  This isn’t something that is going to effect the visuals of that game that badly.  You will probably notice a few more jaggies here and there, something that sometimes can’t be helped.  Large amounts of “AA” are hard to pull off in real time.  Especially on consoles.

It seems like after what they did with Halo 2 and Halo 3, they aren’t showing off anything not in the game or that will be dulled down.  We all remember the epic Halo 2 level from E3 that never made the game, and the Halo 3 reveal trailer that looked 10x better than the actual game.  It looks like they aren’t doing anything of that sort this time around.  That’s good to know.

Bungie Weekly Update [Bungie]