I've played through most of the Empyrean Campaign now, and there have been lots of things I didn't like. Of course, not everything about it is bad, and usually the gameplay is entertaining enough. But it's riddled with minor and major annoyances.

1. The map design is lacking. This refers to the world as a whole, and the individual maps. It's often very noticeable that a map is designed to make you run around a lot and fight a lot of enemies before you reach your destination. Sometimes you spawn somewhere in a corner of the map, and can immediately tell where you have to go with a short look on your minimap because there's a place on the map that's very obviously walled off (or surrounded by water, or some other obstacle) and is a pain to get to. It ruins both the exploration aspect of the game, and the immersion. But then on other hand, there are areas that are the complete opposite - a dozen paths that all lead to the same place, and it's nearly impossible to keep track of which areas you've already explored. This was especially bad at The Breach. With all those paths in the cave, and all those connections between the cave and the outside world, it had me at a complete loss as to where I was supposed to go. After I'd spent a while exploring, I got tired of it and tried to find some hints or a walkthrough on the internet. I didn't find anything. This was the first time I considered to stop playing, because it simply wasn't fun. In the old flare mission, exploring and finding new places to go was fun. Here, it's a pain.
2. The boss fights are horrible. I'm talking about Mex and The Pit here. Being thrown into a locked-off area with an overpowered boss and an infinite number of his henchmen may be challenging, but it's a bad kind of challenging. When I first faced Mex, I stood absolutely no chance. Mex didn't even have to do anything; I got annihilated by all the dragons around him that just refuse to stop respawning. So I gave up on fighting him and went back into the Temple to farm xp and hopefully get some better gear. And I did get some better gear. Killing one of the boss mobs in there dropped some crazy powerful boots. So I go back to fight Mex again, and guess what? All of a sudden the fight is a joke. The number of dragons flying around is seemingly reduced to a third, and Mex's attacks barely hurt me anymore. And all I thought was: This is such a f***ing terrible mechanic. The boss fight was no fun with or without that piece of equipment. This was the second time I almost stopped playing. Fast forward to 7 levels later: The same garbage happens again in The Pit, except this time I can't be bothered to look for that item I need to make this fight a joke. This time I actually stopped playing.

Those are the primary complaints I have. Everything from this point forward are minor issues.

1. Why is it so hard to find adequate gear? For the entirety of the game, I've worn not one, but two +item drop chance rings. Yet somehow I managed to not find a single magician's wand between levels 7 and 12 or so. I upgraded from a purple level 5-ish wand to a white level 10-ish wand. After I got this wand from a mob, I realized that I could've bought one from the merchant in the starter town - because apparently he only starts selling those when you reach a certain level. Why can't merchants sell everything right from the beginning? It's not like you can afford or use the high level gear until later in the game anyway.
2. Why don't you get any skill points for a while? Here I am, excited to level up and unlock new skills, and I realize that I didn't get a skill point. And I have no idea why. Or what I have to do to start getting skill points again. Should I avoid leveling up until I figure out the mystery? Or should I do the opposite, and farm even more xp? Taking away the player's skill points while they're excited to unlock new abilities is both disappointing and confusing.
3. What the heck is up with the lever puzzles? I get it, I have to look for those glyphs/runes/whatevers on the ground. But what do they mean? Half of the time it turns out that I was completely overthinking the puzzle and the runes simply indicated the on/off state of the levers. (Like, flip the ones that are marked with a rune, and leave the others alone.) The other 50% of the time I can't figure it out at all and have to resort to flipping levers randomly until something works.
4. Merchants and money are completely useless. Merchants hardly sell any good gear, and the few pieces of equipment that are worth buying are easy to afford with the mountain of gold you carry around. Giving merchants better and more expensive gear would give the player a means to get equipment if they get unlucky with drops like I did, and it would make it worthwhile to pick up all the money that enemies drop. With 20k gold safely stored in my shared stash, gold dropped from enemies has basically disappeared from my mental loot radar. I stopped picking it up a long time ago.
5. The loot drop rate of chests and barrels and similar objects is just disappointing. In earlier versions of flare, opening chests and barrels was my favorite thing to do. Now it just feels pointless, because most of the time it doesn't drop anything anyway. They don't even drop gold, which would've been a decent compromise between dropping something but not actually giving the player something useful.
6. Where are the ambushes?! Not once has a bunch of doors all around me opened and released a bunch of enemies. Nothing surprising has ever happened in this campaign. Back in the good old flare this happened routinely, and I liked it because it really made it worthwhile to learn a variety of different abilities. In Empyrean Campaign, it's almost like my offensive spells are the only useful ones. The only time something surprised me in the Empyrean Campaign was when a bunch of spikes appeared from the ground and oneshot me. The only way you can ever be in a sticky situation is if there's a bunch of off-screen enemies sniping you with their ranged attacks. Not my idea of a good challenge, really.

To sum it up: My only enjoyment in the Empyrean Campaign is fighting enemies. The exploring, looting, leveling, gearing and puzzling aspects all fall short of the old flare demo mission.