The core problem with Shen is that he really can't get anything out of...well, anything. If he builds AP, he gets a marginally stronger Ult shield and marginally more damage on Q...and then as always runs around doing nothing, only he's also as squishy as hell. If he builds mostly tank, then he taunts, maybe ults... and then runs around doing nothing. If he builds AD/AS he actually starts doing damage, only his AD/AS scaling is worse than even some pure AP Carries. Oh, and he's also incredibly squishy. If he goes Aura support then once again he can do *something*, but once again he's also horribly outclassed by other champions using the same build.
To list out Shen's abilities, he has:
- A short-ranged nuke with an on-hit heal component.
- A self shield that does nothing but self shield.
- An AoE CC gap closer (medium duration).
- A global teleport that shields an ally.
- Bonus damage every few seconds on autoattacks.
How about we compare that to...I dunno, Leona:
- Single-target stun with extra damage (medium duration).
- Armor/MR self buff with AoE damage.
- Gap closer with AoE damage.
- Long-range AoE CC (medium duration, or slow) with damage.
- Passive that makes allies deal more damage from abilities.
Or maybe how about another one of the lower-tier picks...say...Jarvan:
- Short-medium ranged AoE nuke with armor reduction.
- Self-shield with slow.
- Armor/AS buff, with Armor/AS aura and AoE damage. Also functions as AoE CC (short duration) in conjunction with his Q.
- Walls off an area around the target and deals damage.
- Passive that deals a % of target's current health every few seconds.
Can we not see the problem here? Leona and Jarvan are hardly considered the best tank picks, yet just by raw functionality they completely outclass Shen at everything except his Global Ult. Yes I admit that Stand United is pretty strong and technically makes it difficult to balance him based on that (he can flip the balance of any minor engagement) but is that really a good justification to make him incapable of doing anything notable except taunt? He does practically no damage, offers no benefits to his allies past 2 skills (and maybe Vorpal in lane), and one of his abilities is considered to be a blank space on his skill bar.
Probably the best way to start tweaking Shen would be to do something about Feint. Personally I'd vote for the following:
Cost - 40 Energy
Shield Value - 80/120/160/200/240
Damage Value - 60/90/120/150/180 + 0.6 AP; 50% more is 90/135/180/225/270 + 0.9 AP
Duration - 4.0 seconds
Active - Shen enters a defensive stance, shielding damage for 4 seconds. When Feint ends, it deals damage and slows all nearby enemies by 30% (flat). If Feint ends prematurely (eg: broken by damage), it deals 50% more damage and refunds 20 energy.
It would accomplish a few things: give him an extra damage skill, expand his utility beyond just a lone taunt, speed up his turtle slow jungling, help with energy management and help expand his build options.