I think the inclusion of the Hornet could have a pretty dramatic effect on the way the map is played - the ability to evac a flag runner or drop a bomb carrier by air, rather than having to get them out on the ground, can completely change the dynamic of a map, and I'm looking forward to seeing how the ability to do that affects tactics. There also appears to be some sort of EMP ability on the bases now and combined with the apparent removal of the Scorpion I think that's definitely going to give defenders a big advantage, as in previous iterations once a team got an advantage in vehicles it became almost impossible to turn things around barring serious mistakes on their own part.
At a guess, I'd say what really drove 343i during development isn't so much which maps were the 'best', but which are the most iconic: the ones that everyone immediately thinks of when Halo 2 comes up in conversation. Sure, things like Burial Mounds, Headlong and Foundation are generally decent maps which could benefit from a remake, but Coagulation and Zanzibar were always the map that people associated with Halo 2's Big team playlist, and so it makes sense that those are the two which would be brought back, as it just wouldn't feel the same without them. It's the same story with Lockout and Miship, which both appeared in Halo 3 and were remade as official Forge variants in Reach, and yet those maps are still really highly anticipated. Whether they're the best choices for remaking is debatable... but they're certainly among the most iconic, and I'd say with such a small pool of maps, that's probably the most important thing in getting the correct 'feel'.
What I will say is that I'm kind of disappointed that 343i chose to stick to just 6 maps. You can basically split them into Lockdown and Zenith for Slayer, Warlord and Shrine for Objective, and Bloodline and Stonetown for Big Team - and although you could then sort of mix and match a little bit (Warlord and Shrine both work for Slayer, and Zenith could work with asymmetrical Objective), that's a very small amount of variation. This will definitely be made up for by the fact that we can choose any Halo game we want to play, but as it's the newest engine and the most hotly anticipated, I would have liked to see a larger map pool. Here's hoping we'll have a few more maps released for it sometime in the future, and possibly even a few of the more popular maps from other games!