I would like to suggest a slight change that I think would be a general improvement, which draws from my experience in M:tG. There is a good reason to sacrifice it already, but your opponent has almost no reason to try to kill it currently, making it a little too powerful since you are essentially in full control of 2x 2|3 HP healing for all your creatures (for 4
and some damage in the mean time). Maybe it is not as powerful as I feel it is, but I thought of something that could make it still useful but less one sided.
Have the sacrifice effect do the second part of the ability, and make the automatic part only when it comes into play. Thus, it would read:
"When Benevolent Angel enters play, heal your creatures for 2|3 HP. 0: Sacrifice, heal your creatures for 2|3 HP."
Your opponent will then have a chance to react and you will have more reason to use the ability strategically. Take it as you will, I'm not even sure if it will fit on a card.