Just got back from a week in Bar Harbor and thought I'd post my recommendations.
For lobster, I preferred Beal's in Southwest Harbor to Thurston's in Bernard. Though Beal's charges you for butter (!), they (as opposed to Thurston's) offered softshell lobsters, and we found the staff much nicer.
The best lobster of the trip, however, was on the drive to Bar Harbor, at Young's Lobster Pound in Belfast, Maine (on Rt. 1). The prices are right, the lobsters are delish, and the atmosphere is exactly what you'd expect from a Maine lobster pound.
But I digress. Back in Bar Harbor, we had a mediocre meal at Cafe Bluefish. The restaurant was cute in a Sunday-brunch kind of way. But, like I said, the food was merely adequate. I would not go back.
We also dined at Havana. We shared a crabcake appetizer which was fine, but nothing special. My tuna entree was superb. My husband had a vegetarian dish, which I think they called a black bean stew but was equally big on other vegetables. It was extremely spicy. We both had some nice Latin-inspired cocktails. And for dessert we shared a chocolate pecan pie that was quite tasty.
Our best meals on MDI were at the Burning Tree. I've been here a few times now, so I've got the ordering down to a science. The best appetizer, as far as I am concerned, is the curried crabmeat salad. It consists of local Maine crabmeat layered between papadum, with a bit of diced mango thrown in. It's an ample appetizer, certainly enough for two people, but so good that you may wish you got a second one! They have lots of delicious fish entrees, but my favorite dish there is a vegetarian one: the cashew / brown rice / gruyere terrine. It looks like a vegetarian meat loaf, a term that probably conjures in the mind something terribly mundane. It's anything but.
On the dessert front, I've found the Burning Tree disappointing. Your best bet would be to go back to Bar Harbor and join the line for ice cream at Ben & Bill's on Main Street. I tried a couple of exceptional flavors: Triple Chocolate (chocolate ice cream with giant chocolate chunks and huge gobs of fudgy swirls; you might want to get a scoop of vanilla ice cream to balance the intense chocolate moments) and Black Forest (chocolate ice cream with cherries, chocolate chunks, and almonds).
But in my opinion, the best ice cream to be had is just off the island, in nearby Ellsworth. You can't beat the Moosetracks flavor at Blueberry Hill!
One place I think every Bar Harbor visitor goes is the Jordan Pond House in Acadia. If you sit out on the lawn, ask for a table close to the pond and see how long you linger; I guarantee you will find it hard to remove yourself from the incredible view. And the crabmeat rolls and popovers make for a delightful culinary experience as well.
On the way up and back from Bar Harbor, we stopped in Portland and ate at Street & Co. Since we were traveling with a dog and the restaurant has some outdoor tables, it's a perfect spot for us. Both times I had the lobster over linguine, and both times I was not disappointed. My husband had a swordfish special on the trip up and linguine and clams on the way back. The appetizers tend to have too many ingredients in them, so I'd say that if something sounds like a weird combination, stay away from it. It won't be horrible, but just not great. I found their desserts, particularly their fruit ones, much better than expected. A particularly homey peach mango pie was just like (I wish!) mom would have made. Also good was a rasberry / lime shortcake. I was slightly disappointed by a peach/apple crisp, which was short on fruit and long on crisp.
Back to Bar Harbor for a second, I thought I'd point out that the Porcupine Grill is no more. (I saw a recent post by a Chowhound touting it.) It's got a new name and a new concept, but, I'm assuming, the same owners. We didn't eat there, so I can't comment on it. I also noticed that the Preble Grille in Southwest Harbor is up for sale. Oh, and Redfield's in Northeast Harbor is also undergoing change: as of last week, it's no longer a restaurant, but instead a gourmet food store, or something like that. Again, we didn't visit it, so I can't report on its new incarnation.