I'll take a crack at it too for fun. Thematically.
_NOTE for them if they care: In "serious" pve content, gameplay is melee 95% of the time so if you're a melee only person like me dont worry about 'casters' that does not exist here. And you rarely ever have to stand still to do anything_
**Warrior: It's the warrior**
Uniqueness of warrior in GW2: warhorn/rifle/bow/torch/banners/healing
Most common weapon(s): axe
**Guardian: It's a paladin but blue colors**
Uniqueness in GW2: blue fire, traps
Most common weapon(s): sceptre/greatsword
**Revenant: Think of the anti-paladin archetype like a darkknight or deathknight or whatever except instead of having 10/10 points in defense it put more points into agility and wisdom**
Uniqueness in GW2: It's more like a mystic heavily armored monk that talks to dead people in it's mind than a necromantic shadow warrior. You can go from channeling someone like Ghandi to Diablo in a single button press. HAS A RANGED HAMMER WEAPON
Most common weapon(s): sword/staff
**Ranger: Its a hunter but can be melee as well as ranged, has a pet**
Uniqueness in GW2: Healing/Buffing, mid combat pet swapping
Most common weapon(s): Longbow/Greatsword (staff when supporting)
**Thief: It's the rogue, except it can also be wukong or a sniper or a double pistol shooty shooter.**
Uniqueness in GW2: You steal items from people that you can use as skills in combat/guns and bows.
Most common weapon(s): Staff/Dagger/Rifle
**Engineer: This is a pretty unique one, It's like iron man without post-modern technology. Has kits that are extra weapons you can pull out mid-fight but without visual customization options. Swing with your sword, pull out grenades, toss a few, back to sword, ect.**
Uniqueness in GW2: yes.
Most common weapon(s): Sword/Hammer/Rifle
**Mesmer: Another unqiue one. Temporary Clones that either do big damage themselves or get bursted for damage or utility effects. Melee magical swordplay with some range. Pink and purple pretty butterflies.**
Uniqueness in GW2: RANGED GREATSWORD
Most common weapon(s): Sword/Greatsword/Focus (offhand thing)
**Elementalist: It's this games mage class except it's like the avatar and swaps elements a lot.**
Uniqueness in GW2: Element swapping, you get a ton of skills at once
Most common weapon(s): Sword/Sceptor/Staff
**Necromancer: It's the dark caster class except it's also the deathknight in cloth armor**
Uniquness in GW2: tanky as a cloth class, ranged and melee weapons. RANGED AXE. HEALS TOO
Most common weapon(s): Axe/Staff/Greatsword