Walking With Beasts has many masterpieces as well: the attack of Basilosaurus on the Moeritherium, the entelodont battle, the Indricotherium theme, the Smilodon clash, the very evocative mammoth march, the majestic Australopithecus wandering in the plains after being chased from their old territory, and all the music accompanying New Dawn. And the opening theme of course, which rivals Big Al as the title of "the best". Then there's the closing theme which ends with a peaceful theme of homo sapiens watching mammoths march by as they carve artwork devoted to them — ending up in a museum where Branagh warns "no species lasts forever".
Walking With Monsters: The opening theme, the Anomalocaris fight, the Cephalaspis migration, the Jaws-reminding Hyneria attack, the whole Early Permian Period, the relentless Dimetrodon and gorgonopsid attack, the sad Permian Extinction, and the march/river-crossing of Lystrosaurus. And the Evolution theme: it almost makes Monsters seem like a videogame with all the stages and respective enemies.
The music in Sea Monsters is overall great, but the music playing during the mosasaur attack really makes it awesome, and is equally great to the above Ballad of Big Al example. The credits theme is also appropriately scary, ominous, and dark, and really makes you feel like you're going through the darkest depths to meet all the nightmarish monstrosities Nigel meets himself.