Interestingly, Holmes offers up only four types of dragons in his rulebook -- white, black, red, and brass. I can't quite figure out why he choose these four, since they both differ from those in the LBBs and the red dragon is one of the most powerful of all dragon types, so the list isn't based on "level appropriateness." Holmes also extends Greyhawk's notion that many dragons can be either Lawful or Neutral to include evil dragons as well, which, with the exception of the red, can be either Neutral or Chaotic Evil. He also simplifies the roll to determine if a dragon uses its breath weapon from a 2D6 roll to a 1D6 roll. Likewise, the dimension of a cone-shaped breath attack is altered slightly (5-foot diameter at the dragon's mouth in the LBBs vs. 2-foot diameter in Blue Book).
Dragon age categories are expanded in Holmes to account for the fact that monsters now use D8 hit dice rather than D6, so the "very old" and "ancient" categories are new. He also changes the description of the age ranges within each category, so that, for example, an "old" Blue Book dragon is 101-150 years old, whereas he was only 76-100 years old in the LBBs. OD&D has no rules for determining the gender of a dragon, whereas Holmes does, explicitly linking small size with being female and large six with being male. Despite this, there is no mention of dragon family units, as there is in OD&D. Likewise, Holmes dragons, though intelligent, are not explicitly given the power of speech (though it's implied) and there's no reference to their being spellcasters.
Dragon breath weapon damage is tied to hit points, but, like OD&D, there's no clarification as to whether this number decreases as a dragon takes damage. As a younger man, I always assumed that the damage was tied to current hit points, but the text nowhere states this outright. Dragon subdual is significantly less mechanically complex in Holmes, dropping any reference to a percentage chance based on damage done. At the same time, Holmes notes that subdual lasts for "a maximum of one month," something not stated in the LBBs that I can see and that "thereafter it will seek to kill its captor(s) and/or escape." Furthermore, there's no system for determining how much a subdued dragon brings on the open market in the Blue Book, as there is in the LBBs.
In general, Holmes dragons are much simpler mechanically than those in OD&D.
Dwarves and elves include references to the maximum levels possible to them in full OD&D. Fire beetles from Supplement II are included, the first such creature from Blackmoor I've noticed. Gargoyles and gelatinous cubes follow OD&D. Elven immunity to ghouls is noted in its entry but there's no mention of the victims of ghouls rising as ghouls themselves. Giants in Holmes are, more or less, as presented in OD&D and Supplement I. The main difference is that, as with dragons, he makes them all of variable alignment, with even frost and fire giants occasionally Neutral in aspect. Holmes also includes derived from Chainmail to handle giants' rock throwing abilities, something not done in the LBBs, which simply refer the reader back to Chainmail.
Giant ants and giant centipedes get their own entries in Holmes rather than being relegated to "large insects or animals." The same goes for giant rats, which also get a disease transmitted through their bite. Giant ticks follow Supplement I. Gnolls become hyena-men in Holmes. Gnomes begin their sad descent into being also-ran dwarves as well. Goblins follow OD&D, as do gray ooze and green slime; the same goes for griffons. Harpies are roughly similar to their appearance in Greyhawk, but Holmes's phrasing -- "By their singing they lure men to them" -- made me think that female characters were immune to its effects, something not noted in the text.
Hell hounds are as in Supplement I, but there's no note of their being used as pets by fire giants. Hippogriffs follow the LBBs, as do hobgoblins, right down to the reference to their having +1 morale, even though there are no morale rules in the Blue Book. Different types of horses are distinguished, but Holmes leaves out how much weight each type can carry as a load. Hydras follow OD&D. Kobolds are much the same as before, but their description notes that they're "evil dwarf-like creatures [who] behave much like goblins," which is closer to their mythological inspirations than the dog-men they became later. Lizard men are here and follow Greyhawk.