The bosses do need some work yet. As I understand it, they're not actually finished yet, still work yet to be done on them. Normal enemies seem to have more priority for development, which makes sense.
But yeah, the boss ROOMS definitely are a bit problematic.
As for higher difficulties, they arent as bad as they might seem. Like many such games, they simply require practice. The current aiming system does, in fact, work fine with them. But you'll need to get creative with your spells.... simply firing in a direct line just plain will not work in many situations. Which is how it should be. Valley 1 was good at letting you just blast the heck outta everything you met. This one is designed to make the player have to approach each encounter and area carefully, and consider just what the best approach is, or what the best spell is. If you get to an area that you are having major trouble with, consider going back out of it, and switching to a different spellclass and/or different perks that might enable you to get past that spot. Again, this bit is part of the design of the game. It really does keep things INTERESTING.... I liked the first game quite alot, but the simple fact was that you never had to use more than a few spells. This game makes you have to use MANY of them, and be tactical about it.
The strategy bit has been getting numerous changes lately, which seem to not be done yet, so keep that in mind as well.