I've been to butterfly twice recently and must say I'm really impressed with the quality and authenticity of their Chinese food. I spent two months in china a couple of summers ago and occasionally need a fix. I've been traveling to Flushing Queens but have been looking for something more local. Butterfly is the first place in the area that satisfies.
A word of caution: Not all of their menus are equally tasty. The "Szechuan" and "Gourmet" are noticeably more interesting/authentic then their larger regular menu which appears to have the same dishes as every other American Chinese restaurant in America. They don't always give the Szechuan and Gourmet menus to customers (why?) so be sure to grab them on your way in the waiter doesn't supply you with them.
I've sampled the ma po dofu, stuffed eggplant, Szechuan potatoes, and mango chicken.
The ma po dofu was spot on and better then many places i've tried in nyc. The dish was flavored with ground pork, hot peppers, black beans, and sprinkled with roasted Szechuan peppercorn to give it that distinctive burn (buzzing, numbing) flavor. perfect.
The Szechuan Potatoes we also done just right. This is not a vegetable Americans normally associate with Chinese food but I saw it all over China. The potatoes are shredded and then tossed with (hot) fried green pepper, green onions, some other spices and a sauce. The dish had a great "breath of the wok" flavor. The potatoes would be undercooked by typical western standards but in this dish their slight crunch is appropriate (and tasty). The version at butterfly is better then many found in china.
The stuffed eggplant was good but not amazing. Slices of eggplant are stuffed with ground meat (pork i think) and then fried. A sauce (soy, maybe oyster as well) is put on top. I would consider ordering again but only after exploring the rest of the menu.
The mango chicken was done well but is too sweet for my taste. It was served in two halves of a fresh mango intermixed with mango slices and red peppers. Good but (like almost always with this dish) too sweet.
They also have a sushi bar (eh) and like mentioned up top, the standard american chinese menu.
Summary: Great chinese food in Northampton/Amherst area but order from the gourmet or szechuan menus.