So far i have played about 25 to 30 matches with Shen, did win some and lose some. This is my take on him right now.
Ki Strike - Nice passive, quite decent to punch extra damage when being attacked by champions. However the fact that must be a champion attacking you in order to reduce the refresh time makes it less interesting that it should be. The fact is that once people realize that hitting Shen is a bad ideia he will be hit less and less therefor making his passive less effective. It works well with Shadow Dash as the taunt forces you to be attacked thus increasing the amount of damage dished out.
Vorpal Blade - Pretty decent spell. Ok damage for a tank. Healing is decent to help you stay in the lane during the early game. However at late game stages Vorpal Blade makes little diference to the team. Greatest problem seems to be that the effect proc only once every three seconds, thus since the duration of it is 5 seconds at best you will get two procs. This is mitigated by the fact that the cooldown is only 3 seconds so you could use it again before the effect ends, however as i explain below that is impossible due to power issues.
Feint - Excellent/Really Bad ability. This is an excelent ability since it can absorb 310 damage from one attack. Allowing Shen to stay in the fight longer. It's really bad since any damage makes it proc. So if you feint and get hit by a minion it will consume the feint. Also happens with other attacks making it less reliable than we could desire for. All of that would not be a problem if it wasn't for the energy cost. Again i will go over that bellow.
Shadow Dash - Probably Shen's best ability by far. It can be used to escape, to attack, even to some degree to initiate. The only problem is it's energy cost which makes this ability pretty expensive to use and hardly usable more than once during a combat.
Stand United - Also a extremly good ability to prevent ganks, turn the tide of the battle, escape and even to some more creative uses. So far i have seen no problem with it.
Stats - Since Shen is a HP based tank it would be fair that his initial HP and HP gain would be higher than it currently is. I would not mind if he moved a tiny bit faster even if for a tank he moves quite fast. The only reason i say that is because most of his skills are pretty short ranged so short range plus slow moving makes you really need some form of movement boost to catch people. He has decent armor and lacks on magic resistance. I have a small issue with his lack of MR since no items that have it synergize with his abilities or playstyle. So it's pretty hard to put his MR up without sacrificing a bit. However this is understandble as he needs a weakspot.
Energy - This is probably the only real problem i have with Shen. His energy starts with 200 and at level 18 still 200. Even thou some of his spells become cheaper as you level most of the time you will be out of energy to cast more than 3 in a row. That would not be a problem if we could have itens that allow his energy to recharge faster or increase his energy pool. But right now most of the time you will Shadow Dash, Vorpal and if you managed to hit SD you may be able to shield. For the rest of the fight you probably will be out of energy to do anything else.
Bottom Line - I assume that my ELO should be somewhere in the mid range due to my number of victories being only slightly higher than my defeats. So i am basing my thoughts on this tier. For my ELO he seems to be pretty ok, you will score kills, you will support your group and if played well you will also prevent most ganks against your team. This last aspect is very valuable when playing with a pre-made team, if you manage to communicate well 90% of the time you will be able to prevent people from getting ganked during mid to late game stages. You manage to score kills because you have alot more staying power than most characters. Aside from some very strong carries i faced a few characters on 1 on 1 basis and managed to score a kill. If they run i can ghost and shadow dash to prevent them from running away. However the energy problem prevents me from doing something better at late stages of the game. When team fights start to be more important lack of energy just becomes unberable.
Suggestion - Raise his HP a bit to he can be more in line with other high HP tanks and either scale his energy pool with his level or allow mana regen itens to affect his energy recovery. With those two things i belive Shen will be a very decent hero.
Thanks for your time reading this feedback. I appreciate any suggestions and comments.