I find Shen to be viable, and a decently safe pick. He can build armor or MR freely so you can usually just build against your lane opponent and be pretty safe. I've gone up against Riven and Elise both can just built against them and laughed as they try to damage me. He also sets up ganks super easily with his taunt, but your jungler has to have damage or they'll just walk away.
The key to Shen is realizing that he isn't about winning his lane, he's about winning the game. You will end up leaving your lane by Ulting to your teammate, which leaves your tower vulnerable - but if you can use it to save an ally or help them get a kill, it works out for you in the long run.
Like most Full Tanks he needs to coordinate with his team. If you aren't paying attention, you won't be much use. And if your team can't react quickly and capitalize on your engages, then you'll find yourself taunting into the team and then dying.