Classes
Few races but fuckton classes called literally castes in the game.
Fighter, Gladiator, Headhunter (assassin), Knight
Thief, Bard
Cleric, Paladin (Cleric-Knight)
Martial-artist, Sword-dancer (literal translation: Sword-artist)
Witch, Witchmaster (Warlock), Firemage (Firewizard?), Wizard.

Bards are technically crossbreeds between rogues and magic users just like in DnD. In fact some of their stuff was copypasted from there. It's a Mary Sue class for one of the writers as in his novels - some of which predates MAGUS - the main hero is a bard. His personality, behaviour and magic in the novels is clearly based on the DnD description of bards.
Cleric and Paladin subtypes are numerous since every gods have their own. Well some gods only has Clerics, some only Paladins.
All magic-user class has different magics. Bards, Witches, Witchmasters are only empirical-magic users it's kinda low-magic stuff and they don't have a grasp on the Arcane, unlike Wizards who use high-magic, and they have the knowledge about the essence of magic. Firemages are inbetween as they don't have the arcane knowledge but use the fire-magic line of the high-magic. They are somewhat sacral casters as well.
Wizards use mosaic-wizardry, certain smaller pieces are defined in the rulebooks and the players are encouraged to create their own spells from these mosaics or even come up with new ones besides the examples given by the authors.

The Second Code of Law gave new classes, the nomad shaman and the monk, also defined some new Clerics for some gods and gave a longer description, more exact rules for the Firemage. In this case the monk itself is more similar to European monks and not like the chinky DnD monks as these were already materialized in the Martial-artists and Sword-dancer castes.

The Summarium described new classes for non-human races.
Elves got the Preserver with several sub-classes, sacral servants of the elven kalahoras, god-ancestor type ancient elves. Smells like Druid to me. Elf fighters got some specialties and "prestige classes" (in DnD terms).