Personally, I'm still iffy on the concentration mechanic. While I like it as a balancing factor, I think they went a little too far with it; too many spells require concentration, some of which aren't even that viable as combat option. And I hate that the odds of losing a spell when hit is strong, due to lack of constitution proficiency and low AC. I'm speaking from the perspective of a wizard; I sure clerics, with their medium or heavy armor proficiency, can better weather a storm of blows.
Case in point, my wizard character is 7th level, and I've already either lost concentration because my 14 AC isn't enough to protect me from the raging barbarian who decided to focus all of his attention on me last session, or I've had to give up a spell I was concentrating on to cast a more vital concentration spell to pull another players but out of the fire, thus wasting a spell. It's getting old really fast.
Honestly, i wish they would have deleted the getting damaged clause in concentration and just said "you can only have on spell requiring concentration active at a time." Then at least I wouldn't waste spell slots every time an enemy gets clever and targets me rather than the BSF.