Adds some nice stuff like Stormtroopers, brings back the Minister mechanics, allows NV changing and has a ton of NVs, little stuff like being able to embrace the Slovak minority as Hungary, a new wave of crusades if you form Italy as the Papal States, all sorts of stuff. It's less close to vanilla than HPM, but less railroading than HFM. BAI is, in a way, a spiritual successor to /gsg/ vickymod (and does in fact include a lot of events and decisions from that mod). The third mod that deserves mention is Blood & Iron or BAI.

The HFM map is really nice, and I do wish HPM and BAI would use it too. It also changes the map a lot, especially scaling and shape of German minors. It does have some interesting alternate-history railroading branches, which is nice some of them fairly lengthy (ie Rhine Crisis -> Rhineland puppet -> France annexes Rhine -> Austria calls Leipzig Conference and unifies Germany, this takes place over a few decades ingame) but it's definitely a different experience from vanilla or HPM. HFM conversely does a fair amount of railroading. Fixes a bunch of stuff, enhances the game in general, but overall the gameplay experience is still 'vanilla, but better.' HPM is basically like an unofficial patch for V2.

Victoria 2 hfm vs hpm