Halo is at its best when we find ourselves in a large, open battlefield with a selection of guns and vehicles to choose from and a whole load of covenant to take down in any way we see fit.
We like that freedom to adopt any tactics and strategy we like, no matter how brazen and ill-thought out. We like ramming our warthog in to the scarab's shins, and that's what Halo does really well - gives you as much opportunity to mess about with friends as it does to embody a badass super soldier.
What we liked about the first Halo was the fairly large levels that we could drive our warthog around and explore before getting stuck in to a fight. In the subsequent Halo titles, we felt that the levels funnelled us in the right direction just a touch more.
That's not to say all the most recent Halos have small levels - they still contain fairly large areas, but we liked that little extra freedom of the first game. It felt the more sandbox-like, and more like an explorable world rather than levels. Give us some of that again.