We felt the same way when we read Caesar's commentaries and we've tried hard to make sure the new fort and bridge construction features will let you recreate Caesar's strategies as close as possible. However, following on the ideas presented in Jim's caricature essay, this doesn't necessarily mean that you'll be able to build walls in the exact pattern that Caesar did but rather that you'll be able to create fortifications that address the same strategic purposes of Caesar's walls.
I think a hallmark of the Hegemony series is how a relatively small set of mechanics can be used in different combinations across diverse terrain to create a wide variety of strategic situations. So, when we set out to design the new fortification system in Rome we looked at all the ways Caesar used engineering in his campaign and tried to find a mechanic that could represent as many of them as possible. The result is our fortified camp system where you can build supply camps at hundreds of predetermined locations and then optionally fortify and garrison these camps like you would a walled city. These forts can be built in the open like the Romans usually did for their daily camps, or they can be built in constricted terrain to completely block a pass. They can also be built on select river sites to allow armies to cross otherwise impassable water like the Rhine or to fortify a ford to prevent enemies from crossing.
In the case of Alesia, Caesar famously built his double circumvallation wall to protect his forces from the town as well as outside reinforcements. Implementing a ring fort like that would have required significant changes to our pathfinding system and building mechanics for a strategy that was only used once. However, using the common fort mechanic you can effectively implement the same strategy in Rome by building forts across the entrances to the region where Alesia sits. These forts will cut off supply lines to the town while also protecting your forces from both sides.
Similarly, at the beginning of the campaign, Caesar describes the wall he built along the river to prevent the Helvetti from crossing. In Rome you'll be able to effectively recreate this same strategy by building a fortified bridge at the crossing.
As far as the advanced formations are concerned, we're aware those weren't well used in Philip/Gold. They were implemented very early in the design under the assumption they would have a greater impact on combat. We considered removing them when this proved not to be the case, but decided it was still kind of fun to make your units snap into those fancier formations so we left it in there.
I've hinted at this a little in the forums so far, but in Rome we've got some more ambitious plans for the formation system that we're still in the process of testing and refining. The idea is that the formations will also convey some automated behaviour for your units so that a flanking formation might cause your unit to try and move around behind the enemy it's attacking or a forced march formation might sacrifice food capacity for movement speed. I can't commit to this stuff right now as there are a lot of balance and playtesting issues to work through but we'll let you guys know more as we lock stuff down.