1) You are escaping from something, Covenant, planted bomb, flood, what ever. You are riding in a pelican with Rocket or Laser shooting down pursuing Banshees. The rest is based on what the map maker wants to do. This could be a firefight with endless banshees or just target practice where if you run out of ammo for both weapons, you lose :)

2)Like in the Halo 3 mission where you have all these mongooses with marines riding rockets taking down a scarab. Why dont we have a skirmish with mongooses, anti vehicle warthogs, spectres with fuel rod riders and a semi auto fuel rod mounted cannon....etc. Eventually the Covenant or Humans lose and you move on to take the base.

If these ideas are good, please do say. If it sux, please say why so I can think of some other ideas. To be honest, these ideas actually seem fun :)