This is a pretty standard Fighting Fantasy offering (and nothing to do with Amazon's product description). It utilises the common, but still popular, plot of infiltrating a stronghold to slay an enemy sorcerer. Although it doesn't do this as well as other books in the series it still does it quite well. The 'genetic experiments with magic' idea gives the storyline an interesting edge and the use of a WILLPOWER attribute is worked well into this.
There is a selection of well characterised allies to come across; ranging from ancient goblin market stall holders to dwarf gardeners. But your opponents sometimes get a bit repetitive and tedious, generally consisting of bits or assemblies of flesh and corpses or just mere soldiers. Some of the artwork is also a little basic and immature for these encounters. The two major villains are quite well portrayed and contrast well together. The sorceress Senyakhaz is elegant, attractive, cunning and calculating whereas her master, the socerer Xakhaz is a hideous and ravenous amalgamation of body parts. Very much a beauty and beast combination. Xakhaz, statistically anyway, is also one of the most powerful opponents to be encountered in the FF series. If you have collected the correct couple of items en route though they should negate his statistics.
The use of mirror portals, although just used in the previous book of the series 'Creature of Havoc', is still very intriguing. Although they are used to better effect in 'Black Vein Prophecy'. You will need to use them correctly to succeed but in using them wrongly you can catch glimpses of the unexplained and unknown southern land of Zagoula. It would have been interesting to see more of this land (it appears again in 'Portal of Evil' but also in a very minor way).
This isn't by any means a difficult book. Entering the castle the correct way is the only tricky part really. Only one route will get you the items needed to practically ensure victory (and the need for these items is well hinted at in the text). But without them, and with some good dice rolls, you can still reach the end. Although not one of the highlights of the series this is still a solid adventure which is worthwhile and relatively satisfying.