Having read many other David Gemmell books and a fair few other 'classical era' historical books, I can confidently say that this absolutely combines the best of both worlds, and in many ways beats the historical stories at their own game. The story focuses on the character of Alexander the Great's general Parmenion, who comes from a poor, but noble, family in Sparta where he is the victim of racist abuse and attacks for his foreign mother, to becoming Philip of Macedon's number one general and helping to lay the groundwork for one of the greatest empires of the aincient world.
Unlike the sequel (Dark Prince), Lion of Macedon largely refrains from involving many classical fantasy elements (magic, monsters, etc.) and focuses more on the historical side, which may not please fans of high fantasy, but makes the story that much more captivating. The fantasy element largely manifests itself in fortune-telling and predictions of fate, which don't really play a part in the story until Dark Prince.
Instead, the story is concerned with Parmenion helping Philip's small kingdom - poor, weak and surrounded by powerful enemies - to first survive, and then dominate the rest of Greece in the fascinatingly unstable and war-ravaged world of aincient Greece. Not to mention getting his revenge on the Spartan bigots who bullyed him when he was a child.
Although it isn't Gemmell's best book (everyone has a different favourite, but I would place Bloodstone and Winter Warriors highest), it's certainly up there with his very best, and that makes it one of the best of the best in the genre, and well worth reading if you're a fan of any kind of historical or fantasy fiction.