Anyone else do this? Just sit back and watch the AI fight itself? Or do you just wade in all guns blazing?

I nearly always let the groups of enemies thin each other out - plus I just like seeing how the AI works.

If I had to pick favourites...

Halo 1 - probably the battle on Two Betrayals right after destroying PG #2. Also, just before Engineering on The Maw where you can actually get all 3 groups of enemies involved (I believe this is the only part of the game where you can do so).

Halo 2 - the end of Gravemind - 'nuff said.

Halo 3 - probably the run up to Truth on The Covenant where the Brutes fight with the Flood. I usually step in and kill just enough Brutes to allow the Flood to start getting some combat forms up.

Halo 4 - there aren't many enemy vs enemy duels in the game but when the covies chuck in drop pods against the prometheans - that's a pretty good fight.