They work well in the north east but you do have to keep an eye on them for watering needs. They certainly do dry out faster that flat earth. For things like tomoatoes you might even do better in the raised boxes because of the extra heat. Some plants need all the heat they can get in the NE.
I bought my place and they had a hodge podge of raised beds and the sellers said they did well with them. I tore them out because I wanted to go bigger and I had a 5' tractor mounted tiller. I still have to watch my moisture levels as I only have so much soil before shale/slate bed rock. I pulled a lot of it out to do what I wanted to do. We had a fairly moist summer and things did pretty good. I had tomatoes coming out my ears, and cukes too. My buddy came up a few weeks ago and was bitching me out. He still had green tomatoes at first frost, not some, all of them. I had left more tomatoes to waste than he got all year. I canned a lot of them, and gave boxes and boxes away. I had planted 13 Roma San Marzanos and 6 Early girl and 6 beef steaks. Then I had some wild recruitment from what the previous owner had and got a small yield of grape and cherry tomatoes off to the side from when i had been temporarily shoving off the top soil and pulling rock.
A lot of times depending on what your mulch was made of you may have a serious imbalance of something. A lot of times it's an acid level.