The why of fun is a pretty tough thing to nail down. It's very hard to say why you're having fun (or not). What is much easier, then, is to say whether or not you are having fun. And I'm not really having a lot of fun with FE right now. But I had to play the Warlock: Master of the Arcane demo to realize this.
I had a lot of fun discovering what kind of game FE was at first. I was dazzled at every turn by the complexity of its systems and the amount of stuff there was to discover. But a few games in that's slowed down. I'm now starting new games, playing a little, then getting really frustrated or bored and abandoning the game. I thought the 0.9xx series should make things better because it introduced a lot of variety, but if anything it's worse now. I had no idea why that was until I played the Warlock: Master of the Arcane demo, and I think I have a good idea now.
In Warlock, every turn seemed to have a tough, interesting choice in it. Building stuff in cities is a rare opportunity, there's always a few things you feel you HAVE to have, and when you do make a call it's 2-3 rounds and bam the building's there and you feel its impact. Something about the game changed. Spells are super expensive to use but when you do, they have a really big impact that you can feel as well. It's rare that you cast something, but when you do, the game changed.
In Fallen Enchantress, I'm always doing something, but I'm never sure if it's a good idea, if I need to do it, what the effect was, etc. In a word, the game's mechanically muddy. There's a whole lot of buildings I can make from a city, and clearly one is going to be better than another, but I don't really know what I need. I usually have another money, but even if I don't it's not clear what big game-changing thing I could do with money. The best use I discovered is to Rush stuff, but again: stuff doesn't feel impactful. I slowly fall behind the AI, but it's not clear why. Many turns I skip waiting for armies to heal up or units to be built and it just feels dumb: I'm not doing anything, but it's not clear what I could be doing.
And yes of course the UI being very very frustrating doesn't help (and I do appreciate the irony of comparing a game to a Paradox game and saying that basically the Paradox game has the better UI. That's like saying a Michael Bay film has the better plot. Unfortunately it's true.) I wonder if it would help Derek and the devs if we catalogued our misgivings about the UX? Let me try a quick best of list:
* Cities happily idle without warning you.
* Moving multiple units out of a city is retardedly hard.
* Exclamation marks over things you can build improvements on are super inconsistent (sometimes they're there, sometimes they're not)
* Rounds just auto-end with no confirmation
* Map is really hard to read, with lots of "peculiarities" (like monster lairs that extend way beyond the tile they're on, but you can't click on them beyond the actual tile they're meant to be on)
* Adding buildings to a city's queue is really confusing (you have to double click the building, click and place, or click and build. Often I'd click out of the city not having placed the building)
I'm sure there's more, but that's the first ones that come to my mind.
So, TL;DR: while Fallen Enchantress has a lot of decisions for you to make, it's never at all clear what the best decision is, the impact of your decisions is either massively delayed or not detectable at all, and it often feels like there are no viable options on a given round. Everything feels muddy and slow.