I think the lore is great and when you get the spells you need, it is indeed amazing. I fully agree with you on the Curse of Anraeir. In the BRB "open terrain" is a type of terrain like the others, and they spell clearly indicates that ALL types of terrain should be considered as dangerous. Basically it will prevent the unit from moving, unless your opponent really is ready to lose 1/3 of his unit. It's a great spell that gives you a lot of control on the battlefield against hordes.
The Transformation is also fantastic on a Slaughtermaster. One big problem with the Transformation is that it is a RiP spell. So normal wizards (elves or humans for example) will see their Transformation dispelled in the opponent's turn, and will then have to face a lot of attacks coming from the unit he is facing, unprotected. With the Slaughtermaster it is not really a problem, with our WS4, T5, W5. It's like we're still transformed
The problem that I have encountered when using the lore is that it is easy for your opponent to prioritize their dispell attempts, for two reasons.
1. The casting values are high, so it's rare that you'll be able to cast many spells. A good example is Wyssan ; at 10+, you take a serious risk if you try to cast it with two dices, even with a lvl 4. That would end your phase prematurely. So you probably need 3, which is often half your dices.
2. In turn 1 or 2, the Transformation, the Savage Beast, even Wyssan's Wildform need not to be dispelled. So they can focus on dispelling the Curse and the Spear (if needed).
When you are in combat, it's the opposite, because your Slaughtermaster probably is in a unit that is in close combat. Unless in specific situations where you can get 3+ characters affected by an upgraded version of the Savage Beast or the Pelt, they can probably focus on dispelling Wyssan and the Transformation. One character with the Pelt or the Savage Beast isn't probably game changing, so they can let that go through.
So in my opinion, an okay lore with many useful spells, but hard to use against a clever opponent.