Bar Harbor didn't get much accumulation, but the rain, sleet or snow plus very high winds made walking outside painful.
FWIW, participants on a travel forum are recommending against May. They write that you can get some nice, sunny, warm spring days, but it's usually rainy and chilly and black flies and mud are issues. September after Labor Day seems more popular.
They also say Sunday's storm was very unusual. If so, I'd go again in late October. Downside is that it's after foliage season and many places are closed, but there were no crowds and I prefer a bit of a chill. It would be nice to see peak foliage, but that time is likely to be rather crowded.