Being a HALO:CE veteran, I want to share something. We all consider map size to be "small", however we forget the fact that size is relative to the speed at which we move. A matter of fact, HALO:CE had small maps. What made it work was the addition of vehicles, teleporters, and even mancannons in latter renditions. This all compensated for the slow movement speed. The result is a game that felt to be paced correctly.
I think the issue here is that for the scale of the game, certain maps are too small, thus resulting in kills from your rear. That is but one of many symptoms indicating a map design problem. To resolve, I'm not saying make darastically larger maps. I'm thinking of using maps such as oceanfront. As one of the newer maps, I think it is quite well designed, apart from the overwhelming multitude of lanes. The change in the map layout as the game progresses makes the map fun, it's dynamic, new routes are open and others closed, and allows for small pushes here and there as the cranes move the containers to a new location. That's fun and draws players. However, many maps are too small for the speed at which the player travels. Take Mart for example. I can guarantee that this map, as well as Cloud9, comprise of at most, if not all, the times I was killed in the back from moving spawns. That is because these maps are noticeably smaller, as in the area in the middle is smaller. This area is the area where the most action is concentrated in, and having it very close together, we have the pace move way to quickly. This problem of rapid pace agrevates the other issue of too many lanes, thus leading to deaths where someone just moves into the lane you just checked, as I mentioned before.
If the map's "Centre" is stretched out somewhat, or the number of flanks/angles one must watch in any given position is reduced, gameplay won't be as chaotic as it is now. The flow can be reduced to a point where it is enjoyable, but not to the point where you constantly have to deal with 2 opponents at every engagement (that happens 99% of the time for me). Ideally, both changes should be implemented, but if there was one change that is to be made, it is that the number of angles one must watch is reduced. This is not only an easier fix than stretching the whole map, but also allows play to focus in 2-3 key areas, rather than the 5-6 it is now.
Again, I'm not a game designer, I'm just voicing my opinion.
tl;dr We move fast, therefore the map feels "small", in order to fix, map needs to be overhauled; but for now, reducing the # of lanes to monitor at any given time will be the fastest and easiest change to make, and should reduce the chaos.