Mai Thai is the only Thai restaurant in Hanover (and, as far as I know, in the Upper Valley). The food is decent, but not spectacular. The lunch special is one of the better deals in Hanover (for about $6, you can get a cup of vegetarian soup, a vegetable spring roll and a plate of curry with your choice of rice). There is also a lunch buffet, which varies from day to day (some days are more vegetarian-friendly than others).
The service is fairly slow - lunch usually takes at least an hour, and dinner can take upwards of 2 hours. As far as I can tell, the dishes that sound vegetarian don't contain fish sauce and the coconut sticky rice with mango is a vegan dessert. Mai Thai is one of the only restaurants in the area with multiple vegan options, so it's definitely worth checking out if you're a vegan living in the Upper Valley.