I have run plenty of Willpower based Sentinels, Tanks, Brutes and Scrappers even back on live. I really enjoy the hands off nature of the set as it gives me more room to focus on situational awareness. I also like the fact that its not slot heavy and endurance light so I can be more flexible in my build. But it does have to be balanced with Tough/Weave/Combat Jumping and/or Maneuvers for defense boosting depending on your AT and play-style.
The trick to survival is in maxing "Rise to the Challenge" by staying close to as many mobs as possible and finding a way in your build to have a heal or better regen to cover those times when the mobs get lucky.
This does make tanking some AVs more of a challenge since he ends up being the only mob so you lean on resists more. But you can still tank/off-tank pretty well as long as you avoid the Alpha Strike. Plus some inspirations/power selections can plug that hole if you have to tank you more difficult AV.
In the Sentinel forum there is a write-up on Willpower that I think has useful info for all ATs interested in Willpower.
Umby