One obvious point with focussing on aberrations is, well, they don't really have a unified theme like dragons and undead do. LoM has risen to this challenge by setting out in the book individual, self-contained chapters on each of the main aberration types: aboleths, mind-flayers, neogi, beholders, grell and a new type, the "wearers of flesh". There is also a chapter with Monster Manual-style descriptions for more aberration types (including more beholderkin, ithillidae and so on) and a final chapter, setting out stuff for "aberration hunters", i.e. stuff on killing aberrations, with items, feats and prestige classes.

I have to say, this really is a good book. Because they have gone for the individual chapters, there is lots of very good information in bite-sized chunks, redolent with adventure ideas and general nastiness for ruining your players' day (as with all of these books, they are mainly aimed at DMs) without it being buried and a little hard to find in the more "normally" formatted books. There is a very high "evil chuckle" factor for each of these, and it's also quite a good read. Obviously, there are some less iconic monsters included (I like the grell, but I was surprised that they got a [good] chapter of their own) but on the whole the suspects you would expect to see are there. There are guidelines on advancing the beasties too, with some monster prestige classes or class advancement options and monster feats, so you can tailor your aberrations to the party. And each chapter has an adventure site (or more than one in some instances) thrown in.

The first chapter, which I initally didn't bother to read, also has some interesting nuggets. In particular, it suggests how to design a "horrific" campaign instead of a heroic campaign. A heroic campaign is the "standard" design with ELs roughly equal to the party's level. A horrific campaign turns this on its head: the first encounters are way in excess (by +3 to 5) of the level of the party to shock the players out of their complacency (the actual characters might not survive). Subsequent encounters are more in line with the characters' level, as they gradually uncover the hideous conspiracy to drag us all into otherworldly madness, and then the final encounter is also deadly (EL +5 or so) to emphasise the terrible danger of the threat. This is suggested as a model to shake up the players a bit and make the aberrations involved more terrible and memorable. However, as a concept it works equally well with other monsters, like intelligent undead (a cabal of vampires for example).

I was sceptical of the "new" aberration (the above-mentioned wearers of flesh) but they are a pretty good addition (and really unpleasant, like perambulating intestines - urgh!) with good possibilities. They also have the benefit of being new, so your players won't actually know what to expect, and so could be a very memorably surprise. And, as they are sort of "body-snatcher" style monsters, they could form the basis of a really good campaign with a mystery and/or horror basis.

The monsters chapter is OK, although not all of the monsters are that compelling. And likewise, the aberration hunters chapter is OK, but nothing special (and most of the prestige classes are a bit samey - quite a few knightly orders bent on slaying aberratons). These two final chapters are a bit flabby, particularly in comparison with what came before.

Nevertheless, this is a great book. First chapters: five stars easily, slightly let down by the later ones.