And what I enjoy about Halo 2 and Halo 3 is the way encounters reset if you don't take out your enemy. Now, it's true that in those games there's an underlying health recharge system, but it's not a significant factor in gameplay because it's not exposed to the player. Combat cycles are swift and frequent. I like the focus on combat and objectives, and adding in the "I'm hurt so I need to run away and find a health pack" mechanic breaks that and takes me out of the fight to scramble for a band-aid. I think it hurts the flow of combat in the game.
To be clear, it doesn't hurt it much. In MP, your health doesn't matter that much because if you lose your shield, the primary threats are grenades and headshots, neither of which will care particularly about your underlying health. In the Beta, I only picked up a health pack if I came across them. In Campaign, I do not like health packs because of the check point system; getting a save right before a tough encounter when your health is low and no health pack is around sucks. And I liked never having to worry about that in Halo 2 and Halo 3. So I'm sad to see that return. But like I said, it's not a huge deal.