Hannibal at the Gates fails to make any meaningful attempt at recreating the actual Second Punic War. That is the real purpose of a mini-campaign, to be a focused map and a focused campaign based around these historical wars. As just a sandbox, it plays no differently than the base game.
The technology trees are absurdly lazy and poorly designed, being completely incoherent. Multiple turns per year advertised as a meaningful feature, as with seasons and attrition. TPY, seasons and attrition all should have been part of the Grand Campaign.
Massilia got their new roster (and remain unplayable), but E mporion, which is their own colony, yet has the old, unfinished roster. Syracuse is a pathetic copy of Athens, literally “stealing” the “unique to Athens” Thorax and Thureos Hoplites, without having any of their own unique units (Factional Mercenaries are not relevant in this regard).
The Celt-covered Iberia prior to release was pathetic, the Iberian culture (and unique units) should have more or less been in at release. Despite the importance of the Etruscans, Samnites and Numidians in this campaign, they retain boring, unfinished rosters. The Etruscans do not even field Etruscan Hoplites, nor do the Samnites field Samnite Warriors and Campanian Cavalry.
The Boii of this campaign are related to the Boii of the GC, and should have been playable with their proper roster, for a unique start and roster. Likewise, having a Numidian faction and Italian faction playable would have meant creating meaningful rosters for them and enabled unique starts. It is a shame that the separation between “Latin/Roman” and “Italian” culture did not go into the GC, where the Samnites should have been able to rebel in southern Italia or northern Magna Graecia.
The Greek theatre is also entirely missing, with Terra Incognita taking up the East, leaving Rome completely safe in the Adriatic. During this era, Rome was beset by Illyrian pirates and Macedon was in alliance with Hannibal, and had they broken through the Roman allies in Greece, could have turned the tide of the war, but nothing interesting is done. For a game based around the concept of changing history/alternative history, leaving out the Greek theatre was a big failure. Hannibal’s time in Italy was spent raiding, yet he has no ability to Loot settlements as barbarian factions do or Liberate (which would simulate his turning Roman allies to his side). For some absurd reason, the Civil War mechanic is also in this DLC.