I live in Maine! Moved here about 7 years ago.
Some of these have already been covered, but here's my list:
Blackflies! Just when it's starting to get nice out. But they're not much worse than mosquitoes, etc. Of course, we have those too. The ticks are also a pain, and have you heard of brown tail moths? Those are the absolute worst, and getting worse every year since they're spreading more widely.
https://www.maine.gov/dacf/mfs/forest_health/invasive_threats/browntail_moth_info.htmLow diversity and also the oldest population in the country. Online dating sucked, but I did meet my now-fiance eventually!
Healthcare is sparse and often not very good. Expect to have to go to Boston for anything fancy.
Compared to the other places I've lived (Ohio, upstate NY), there's a lot more very rundown homes. And I'm not talking just old - think appliances, actual trash, furniture, mattresses, etc. On my drive to work, I pass about 5 couches and 2 mattresses, all of which have been in front yards for at least a year. Within a mile of where I live (pretty rural but near a bigger city) there's at least 4 buildings that have collapsed/burned and haven't been taken down.
Speaking of rundown homes - the vast majority of houses are really old, and not in very good condition. It's easy to buy a 100 year old house and sink a ton of money into it.
Everything seems to be an hour away. For someone who doesn't like driving that much, it's a pain.
A lot of roads aren't very well maintained. There's a lot more patching and other solutions that only kind of help, vs. total resurfacing like I was used to in Ohio.
Too cold for stone fruits like peaches, apricots, and cherries to grow easily. I miss that from my upstate NY days. But the blueberries are great!
Fewer options for good ethnic food, Asian grocery stores, etc. Plan to have to go to Portland for these things. (I live about 2 hours from Portland.)
More power outages that last longer than the other places I've lived. But fewer natural disasters overall!
Not much nightlife, if you like that sort of thing. (I don't.)
Slow-ish internet, and not many options for providers.
Now to be fair to my state, some good things, some of which surprised me when I moved here:
Fantastic local food scene, including wonderful vegetable farmers, cheesemakers, bakers, etc.
Great restaurants, although see my above point about driving an hour to get anywhere.
Great local theater, and more options than I expected.
Plenty of liberal people and at least in my circles, plenty of acceptance for LGBTQ+ folks, etc.
Wonderful nature - mountains and rivers and lakes and the ocean.
Overall, I really like living in Maine. I'm planning to stay here until I FIRE at least, and if we leave, it'll be to move closer to family, not because we want to get out of Maine. It doesn't feel like I'm on vacation all the time or anything (maybe if we lived right on the coast?), but there's plenty for us to do, it's nice and quiet, and I've made some great friends and like my coworkers.