I would switch the guardian angel too a dwarf panzerguard the angel is just slightly better but it still three spellpoints.
I also suggest that you add either animate dead or ziggurat of undeath for a nice late game andvantage.
You didn't include cloak of shadows which I think is solid in these kind of books.
Personally I always include two walls in my builds because they can be used for so many different situations.
Lastly the zombie crawlers are useful but I don't think you should have six of them. They are sheep but you can't rely on their damage.
I prefer by far the Angel. Aegis can't be bypassed by Piercing. Flying can be useful to inder/attack flying units. The 2 hp healing make him last way longer than Panzerguard and it make him able to live even if Idol is out.
Most of times I find Cloak of Shadow "useless". I either do not cast it early enough and I get targeted anyway or opponent stick very closely to me and it become pointless since I am either at 0 or 1 range anyway.
Most of times Walls will inder myself. Yes they can be useful in some situation, but often my opponent will use it too to block LoS or run around to avoid zombies. So I prefer a clean arena.
Zombie Crawlers are Shoggat's food and they are nice to get out for 2 mana from Libro when I do not have mana for a bigger zombie. In 99% of my games I get at least 5 of them out.
I had Animate Dead in the book before, but I found out that I prefer to spend the mana on a real zombie than getting a damaged Slow creature that will maybe hit 1 time before the game is over.