Holy crap, Consecrated Ground: L5 Cleric Daily, restores hit points whenever you start your turn in it and you're bloodied. So far so good. Except that it's "regain hit points", not "regenerate" (which stops working as soon as you're at 0) so it works even when you're dying. And by the healing rules, if you're healed while dying, you go up to 0 hp and then regain the given number of hit points. So even if it's only recharging 1 hp per round, it makes you unkillable - you're dropped to -ve hp, fall down in the zone, and when your turn begins you're automatically back at 1 hp and just prone.
I could live with that, except that the obvious tactic - kill the cleric so they can't sustain the zone - won't work. The zone doesn't disappear until the end of the turn that the cleric fails to sustain it, so if the cleric is knocked below 0, on the beginning of their turn the zone heals them and then they can sustain it again.
The drawbacks to relying on the zone are: it's pretty small, and you're only safe while you're in it, and the cleric can't move it very fast. So if you're in an open map with mobile enemies who can hit and run, it's really hampering to have to stay in it. But if you can set it up at a choke point and set your defender and your cleric inside it so nobody can pass, it's ridiculous.
I don't object to the idea that this can bring people back from dying, although that's pretty powerful. What I object to is the self-perpetuating circle where you target the cleric to take out the zone, but the zone heals the cleric so you can't take them out... It just feels really cheesy.
So I can think of two ways to fix this:
1. Add a clause saying that the zone only grants hp if you are bloodied and above 0 hp (like regeneration). That would make it much less powerful, just a lasting source of moderate healing.
2. Declare that the zone (and possibly all powers that must be sustained) ends if the caster is knocked unconscious. That way it can raise everyone from dying, except the cleric. When you have Consecrated Ground on, it becomes vital to protect your cleric. I like this because it's gives more of a tactical edge to having the zone.