Halo 3 styled Invisible barriers were fine with me. Matchmaking games, it prevented anyone from leaving the level, whether by accident or to cheat. In Forge, it gave new spaces to create, as the death barriers were usually a good distance beyond the Invisible barriers. Standoff, Sandtrap, Valhalla, Highground are names off the top of my head that had fun custom games with custom maps outside the levels. A lot of levels just had cool small "hidden rooms" you could manage by getting outside the invisible barrier.
With a soft kill zone (10 second barrier), it allows for more maneuverability in vehicles, and in certain cases, your spartan. It also prevents anyone from cheating, by getting outside levels and into hidden/exploitive spots, as their is no way to survive this barrier. But then I look at the Forge and custom game aspect of it, and you can no longer create those maps that benefited form the extra space above the levels, because you have a 10 second kill zone in place, so you are always forced inside the map with no exploring outside, which may seem like a nitpick, but it did add many hours of entertainment back in Halo 3's days.
Either way, Im honestly fine with both. I'd prefer Halo 3 styled again, but I wont really think twice if it doesn't happen.