Crusaders of Light offers three classes and 9 possible specializations/sub casses via the Path skill tree. A forth has already been announced: Paladin.
Generally speaking, each class has two different paths for specialization and one third path directly targeted for PvP. But since the latter are less viable in PvE, they do have a hard time of getting into higher level raids. So it is not advised to take those paths yet, since levelling up and getting new equipment is really hard without PvE at the moment.
Main article: Warrior
'The Warrior is a powerful melee combatant, with the ability to both deal and withstand great damage. Able to draw their enemies close and pummel them with mighty blows of their axes, a Warrior staring you down is reason for any Hero to tremble.'
Warriors can further specialize, with Executioners being able to deal huge bursts of damage. This is the offensive oriented choice for the warrior class. It's DPS is roughly en par with the Ranger's Scout, but also has huge small AoE output to stacked up mobs.
Gladiators are more adept at mitigating their foe's power and withstanding even the most brutal assault. Especially in the end game, this build choice is particularly valuable due to its sturdiness. This makes the Gladiator best suited what is usually called a tank in MMOs.
Fang of Titanus
Finally the Fang of Titanus is the master of the battlefield, able to disrupt their enemies plans and turn their strengths against them. PvP is the best place to be for this path choice. It excels there, but pays for that with less use in the PvE portion of the game (namely: raids).
Update: The big patch/update on 3rd July 2017 nerfed the shield removal skill and the fear reduction
Main article: Ranger
'The Ranger is a deadly damage dealer, able to strike down foes from afar with bow and arrow. In tune with nature and able to call upon the spirits of the forest, the Ranger strikes from the shadows to defend the light.'
Rangers have a number of paths available, with Forest Guides being the premier archers amongst them. No matter how far your enemy may be, as long as there is a clear shot, a Forest Guide can hit their mark. This is the PvP focused path of the Ranger.
Scouts are brutal fighters as well, with a focus on dealing massive damage all at once to overwhelm their foe’s defenses. DPS is all that matters for this choice. The Scout's chances for critical hits are enormous and can be raised through passives even more. This makes the Scout the bread and butter for any larger raid.
Animal Tamers forgo some of their prowess in archery to instead grow closer to the natural world and utilize powerful pets to accompany them in their adventures. Thanks to their party buffs, the Tamers are getting more important the further the game progresses. In later stages a Tamer per group can mean a substantial upgrade for the whole group - especially in heroic and team raids. It is hard to warrant more than one per group though, if the two tamers are not used to skill juggle effeciently since their abilities don't stack.
Main article: Mystic
'The Mystic commands arcane energies and has the power of life and death at their fingertips. Able to shield allies from damage, heal wounds suffered, and call down the wrath of the heavens up on their foe, a skilled Mystic is the difference between victory and defeat.'
Verity Spirits take a more balanced role, maintaining a strong ability to heal but also utilizing their powers offensively. This classe is focused on a lot of AoE upgrades and therefore is best suited for (mass) PvP and areas where a lots of mobs have to be killed fast. The daily event Protect the Relic is one of those situations, where this path excels. But since it is less usefull than the other two paths in boss fights, it is not recommended to get this path into high levels.
Finally those who chose the route of Magellana's Judgement are capable of inflicting crippling damage that persists even after the Judge has turned their attention elsewhere. This path is basically a worse Scout DPS-wise, but with the ability to still be able to decently heal. So it is more versatile, but not as effective when compared to the Scout or Executioner in damage output.
Mystics can further specialize, with Sheperds focusing their efforts on keeping their allies standing. This is the typical pure healer build. It is needed eveywhere, although only in a quantity of 1 or 2. So the shepherd has a similar fate like the tank (Gladiator), since a heroic raid will always need about half a team of DPS oriented paths, but never that many healers or tanks.