If we're counting engines, we should include Marathon.

But seriously, Halo Wars, Halo 3: ODST, and Halo: Reach were more like prequels to the original Halo trilogy. They never told the story post-Halo 3. 343 Industries is now taking center stage with a continuation of Halo 4-6.

In other news, I can't say I'm pleased. Given the direction Bungie took with the last few games, perhaps a new face will make us feel young again and give us the same joy we had back in 2001. We'll see.