Gus, I haven't played the expansion yet but was halfway through the final mission when I stopped playing. I had bought it at release.
It's difficult to rate the game as someone who has played the original Fantasy General, as FG2 is both a true sequel as a step back at the same time.
Some units have special abilities or special attacks, heroes can pick skills and items can be given to units. Some units had special abilities in the original as well and of course there were items too, but they work a bit differently here. In FG, the majority of the items boosted stats or gave units a new kind of attack (giving an infantry unit a magical crossbow gave it a ranged ánd a melee attack, which made ranged items rather overpowered). In FG2, items offer usually small modifiers to various stats (higher morale, decreased chance to suffer kills and so on).
The addition of mana points means you can't use all special abilities/spells each turn, as most cost mana.
My main issue with FG2 is that, initially, it's mostly a ground game. There's little combined arms and there's no vertical component (there are only a handful of air units, but most of them only appear later on or not at all if you don't use summons). You start with infantry and skirmishers/archers, and that's it for a while.
What also isn't really made clear (well, not at release but maybe a tooltip was added since then) is that you need to charm units in order to be able to summon them with the wolf mother. If you don't, the only air units you'll potentially be using will be a (hero on a) dragon and potentially a hero on a pegasus, as well as potentially some ravens. It's very easy to miss the possibility to summon aerial units entirely. The AI tends to use numerous flying units, with stronger ones appearing when you're dealing with the Empire.
As, like in FG, you ideally want single entities to take the most damaging hits (because single entities like heroes always heal back to full strength when resting and don't require replacements that cost resources), the game can be a bit of a puzzle early on due to your limited options.
With certain summons, either magically with one of the heroes or through the wolf mother, the game becomes a cakewalk. Example: the spitting spider could, at release, spit a web 3 hexes (each turn, no mana cost or cooldown) which would glue a unit in place. With 3-4 spitting spiders, you could essentially nullify all enemy heavy hitters. Another option would be an eagle bear spam (but that isn't very cost effective in terms of mana) or summoning lots of spirits with one of the heroes (I didn't take the "summon spirits" part of the skill tree for that hero, so I've never used them).
All of that, combined with a limited unit selection (and limited enemy variety), means you'll be doing the same thing throughout most of the campaign. There will be points when new strategies suddenly open up, but the final missions become a bit of a chore. FG did a better job due to subtly changing enemy variety on each island.
It's been a few months since I played it, and the new expansion looks interesting, but whether you'll like the game depends a lot on what you expect. It feels like one of those modern kind of games where it looks like you have more options than in other games, but in practice it's a more streamlined game than comparable previous games. Panzer Corps 2 might give you the same feeling, incidentely.
