What this book allows you to do is add unridden monsters into your armies again. Way back in 5th ed you could add unridden monsters to any army which added a bit of a random fantasy element to procedings. I still have some monster models from this era, my dragon (above) and manticore (below) and I'm incredably chuffed that I can use them in my armies again. It also allows some of the bigger recent cool kits (such as the araknorok spider) to be used by anyone (probably a sales ploy, but a good one). I'm not sure about game balance, but the modeling and collecting possibilities are excellent, and I'm trying to work out an excuse to add a monster to my dwarf army. The other great thing is that they've released some fantastic new monster kits (I'm very tempted by the chimera in particular) and are even rereleasing some old classic minis (suprisingly including the Chaos Dwarf Lamasu and Great Taurus monster, although without riders) and reimaginging of monsters long thought gone (e.g. the Cockatrice) this is the part of the release I'm most excited about. The only problem I see is the price, the kits themselves I think are reasonably priced, but the book is £30, which is a lot, although I'm sure the production will be excellent. I really want to add monsters to my armies though so I suppose I'll have to get it.
Anyway with all this talk of magic and monsters I've added a few pics of wizards drawn from my collection.
Grey Seer Thanquol & Boneripper.
An ancient Grey Seer and a Night Goblin Shaman from the Battle of Skull Pass boxed set.
Two Dwarf wizards from way back in 3rd ed.
Two human wizards, on the left the Mordheim special character Nicodemeus and on the right an Empire wizard made from the plastic wizards kit.