Shen needs a full Rework
I don't know about anyone else, but I think Shen right now is really bad thematically and has a boring, hit-or-miss kit. However there is a direction here in Shen that isn't bad, and could be very good. The concept of a "tank ninja" is really dumb, but the concept of a "defensive ninja", something like a body-guard which Riot made mention of in the patch-notes, is valid.
Drop Defense Scaling for Defense Utility
Stacking up Health, Armor and Magic Resist just isn't what first comes to mind for a Ninja. Instead of stats and shields, Shen should have abilities that defend in ways similiar to Yasuo's Wind Wall. More interesting and thoughtful gameplay would also be nice. A ninja is about subterfuge, plotting and ninja bullshit magic; not sitting in top lane as an unkillable meatshield...
... with a Taunt? Really?
Of all the possible things you could do wrong as a ninja... This is probably #1. Again, as a body-guard style ninja, something that keeps the heat off your allies is not a bad idea. But a taunt is. When I play as Shen and land Shadow Dash, I don't feel like "Shen the awesome Ninja", but "Shen the okay tank". What's worse is that this is the sole ability Shen has that feels like a real moment of power, and if you miss it you just feel like an idiot.
What should he do, then?
Here is what I see as core features of Shen's identity that should stay;
-Teleporting in to assist an ally -"Get off my shit!" moment that maintains the point of Shadow Dash, but is not a taunt, maybe something more along the lines of being a scary Ninja (hint) -A throwing blade to add some range and poke -Sustain and defense for himself in lane
Here is how I would translate it...
From Stat-Man to a true, blue Ninja
Q: Keep his Vorpal Blade - The healing mark is not a big deal, but still feels a little weird and borderline useless late-game. Let's drop the healing mark, and add some more damage to this. Make it a skill-shot if necessary.
W: New function for Feint - This is one of Shen's defensive abilities, but is just shield right now. The new ability could do something like Fiora's parry. It blocks a basic attack, and then Shen poofs into stealth briefly to avoid further harass or look to continue a trade on his own terms. Shen could gain a moment of health regeneration while in the shadows, sustain moved over from the Q.
E: New ability "Intimidating Glare" - Shen now Fears a target enemy away from himself, AND away from the ally he has Ult'd to. This could remain a line skill-shot.
Now for a version of his ultimate that really feels like a Ninja's Ult, and not just a better summoner spell;
R: Stand United - This remains global, but when he starts channeling, Shen drops 3 Twilight Clones around the targeted ally. The clones deflect small projectiles in their radius (ranged autos, Ezreal Q, Ashe Volley arrows, etc.). Clones will also automatically attack any enemy champion in this radius (like Azir's soldiers).
When Shen arrives at the battle, the Clones retreat into him as Ki, and Stand United can be cast again 3 more times to send out the clones for repositioning.
Now the Kit is more in line with a Ninja thematically, and does not encourage building tanky. Shen is dangerous at all times with a more powerful Q and the ability to turn a trade around with W. His sustain is more conditional and can be played around by the opponent (trade with him until he tries to Feint, then move back).
EDIT: Shen players will know that feeling when your ult'd target dies anyway and you can't TP...
