The Guardian is perhaps the strongest of the game's professions and the one with the fewest issues. The strengths of the class lie in its incredible bunkering ability, utilities, weapon skils, and group support, as well as its good damage potential.
If I were to identify a weakness, however, it would be the traits for the most part.
This is the combined opinion of myself (a Thief main) and a friend who is an avid Guardian player.
Zeal is mostly solid, but:
Symbolic Exposure needs improvement. 1 stack of vulnerability for 3 seconds per pulse is only relevant in PvE - and barely at that.
Improve scepter and focus trait support.
Combine signet traits to improve them and open more trait slots.
Add some cooldown reduction to Powerful Blades.
Improve trait support for the Torch.
Combine Meditation traits to free up trait slots.
Up Retributive Armor to 10%. At 5%, it is worth approximately 3% crit chance with high toughness - pitiful.
Improve Mace support by adding some cooldown reduction to the trait.
Glacial Heart doesn't really add anything to the hammer. A chill on a long cooldown that you cannot control is redundant and often useless on a weapon that already has high crowd control.
Fix the "immune" bug on Battle Presence.
Combine shout traits.
Combine symbols are larger with symbols last longer.
I pretty much love this line as is.
Smite should be a symbol (with no change to its current function). This would allow for trait benefits on the weapon.
Main Hand Axe
Guardians currently lack a condition damage weapon. They rely on burning as their sole damage condition. A bleed-stacking main hand weapon would alleviate this.
Two-handed 1200 range weapon that specializes in piercing shots and vulnerability.