Firstly
1. The basic story is the same. The Ellcrys is dying and they need to save it, otherwise bad ass demons will escape the forbidding.
2. I love the opening sequence which shows the back story of the four lands - ie the North American continent had a apocalypse and then the other races with the exception of the elves evolved from the humans at the time. There are also nice nods to this back story with them passing by the ruins of what looks like motor vehicles and Will wondering how the old humans created such things.
3. The Dagda Mor was a druid. WTF? In the books he was the most powerful demon in the forbidding. Of course, since he is now a druid, they have to sort of explain how he ended up in the Forbidding, since he kind of would most probably have been born after the banishment of the demons.
He is also somewhat less powerful relative to the Ellcrys and more powerful relative to Allanon. For example in the book he was free to physically go places despite the Ellcrys being not dead yet. Here he is explicitly stated he can't leave his place but can only send his henchmen out. Also in the mind fight with Allanon he seemed more powerful. In the book they seemed evenly match, with Allanon finally gaining the upper hand, killing the Dagda Mor and breaking his staff. Its stated that Allanon was only able to get back to the Elven lines after this battle by sheer will power.
Not too optimistic for an Allanon vs Dagda Mor fight.
4. The fury seems much more powerful than in the books. Namely they are much bigger.
5. Battles - one of the highlights of the Shannara series is the dramatic battles between opposing armies. Obviously with the television budget, that might be hard to show. However now that they mentioned the Dagda Mor won't come out of his hiding spot, it makes me less optimistic of such a thing. One of the climax of the battles include Allanon killing a dragon by causing some rocks to fall on it from a nearby mountain and his fight vs the Dagda Mor, with the latter flying on top of a giant bat while Allanon was perched on a giant raven.
Hopefully they do some sort of battle.
6. Allanon you stag - nice addition to the mythos there.
7. John Rhys Davies - obvious an example of Dwarven cultural appropriation here.
But damn, that guy makes any role awesome.