I pray to whatever gods are listening that Halo 4 never has that on-rails shit again. It was by far the biggest disappointment for me, beyond the extremely lame script.
I saw those moments and was so disappointed; they were such a lost opportunity. The same terrain tackled on foot would have been awesome, and added a lot of play time to a short campaign.
The Exodus one I think was easier to justify, since it was more about selling the overwhelming odds and sense of hopelessness of the siege, one of the only times in the game that Bungie managed to do so - but it still should not have been on rails. Imagine if that part played more like the section on The Covenant from Halo 3, where we take the Hornets along the coast to one of the shield generators.
The one on Tip of the Spear, though, was a very bad idea all around. We spend half the game avoiding AA guns - including the very start of the mission - then decide to ride through a valley filled with them. Even setting aside the memorization based gameplay, the decision to fly through there gives me fits every time.
Hoping for no on rails content, and minimal QTE style events; we've already seen a few.
Kind of like Halo 3's campaign?
Halo 3 has very few siege sections. Offhand, I can't even think of any, though I'm sure I'm forgetting a couple. That game had a great sense of forward progress - The Ark and The Covenant, The Storm. I can't recall ever stopping dead for some door that won't open, or elevator to arrive.