Right now, I am playing a guardian for the beginner box adventure, but I also GM'd a level 5 Guardian in Scenario 1-17: The Perennial Crown Part 2 during PaizoCon! Here are my initial thoughts:
-Hampering Sweep is way too powerful. The fact you can just prevent all enemies from moving out of your reach is too busted. I know I see a lot of people wanting this as the class feature compared to taunt, but this would need to get a rework. Perhaps an enemy can attempt an escape check against your class DC with the current feat. Critical failure means not moving, failure you treat the movement as greater difficult terrain, success is difficult terrain, and Critical Success the enemy is not hampered by the guardian and can move as normal. We could have it be in sync with the taunt ability; the enemy subject to the guardian's taunt is hampered until the start of the guardian's next turn. This way, the guardian is concentrating on one person and not an entire army within reach. We can change the number of actions it takes for the guardian. Two actions to hamper an enemy, or the guardian spends their entire round preventing a select--not all--couple of enemies from moving away.
-With a tower shield, the scenario guardian was able to spend two actions (shielding taunt and take cover behind the tower shield) and raise their ac to Thirty! Combined with a third action of hampering strike, the Webhekiz encounter did not feel fun to run. Sure, a taunted enemy had a +2 to strike the guardian, but there was no way any of the Palace Guards (Tier 5-6) were able to hit the guardian outside of a roll range of 18 through 20. King Webhekiz had a better chance with spells that forced saves and a 15-20 range of success with his Striking Scepter, but not a huge chance. I think I was able to do damage to the guardian in the scenario because of the obstacle failures in the beginning of the scenario, the King's lightning bolt, and I was able to hit with Qxal's Avatar (+20 to hit). Sure, the guardian did have to spend their entire round to accomplish this feat (which a 30 AC is impressive on its own and this is the fantasy of the guardian), but the guardian should not be able to be to prevent all creatures around them from moving away and be able to prevent a lot of hits with a high AC—it doesn’t seem fair to the GM.
-Taunt, conceptually, is cool, but I feel like it is missing something to make it a great class feature. Perhaps we can add “Guardian tactics” like “Come at Me!” (one or two actions) Prerequisite: Enemy subject to the guardian's taunt failed or critically failed: A creature that failed or critically failed a will save against the taunt must make another will save. Failure means it must try to strike the guardian next round, critical failure means it must spend its entire round coming after the guardian, success gives the creature a +3-circumstance bonus to hit if it chooses to strike the guardian with any of its attacks next turn, and critical Success is like the success condition but with a +5-circumstance bonus. The numbers are high with the success conditions, but it incentivizes the GM to target some of the “Tower-shield Sallys”, and the guardian can prevent their allies from being hit by making them an easier target. You can add other abilities like this to give the taunt something more where failuire does what the guardian intends, and success may punish the guardian for their reckless tactics.
Overall, I do love the guardian, but I want to make sure the guardian is fun for the GMs to run as well.