My daughter and I spent a Tuesday overnight at this Inn, the week pre-Hurricane Irene, when the weather was exceptional and the island was jewel-like in all its glory.
I was pleased to be able to reserve any room at all on the island with only 5 days lead time before our departure.
Honestly, for the money, the room is simply unacceptable for the moldy tile and broken apart, cheap vanity in the bathroom; in addition to one lamp switch being completely broken, and a non-functioning outlet. If it had been hot, we would have suffered mightily without AC.
On the other hand, the room itself was a bright, cheerful yellow, and had nice old pine floors. The room was CLEAN. And while the bedroom was small, and the bathroom tiny, we felt comfortable overall.
The young, front desk staff were very nice. The complimentary continental breakfast had orange juice, bananas, melon and yogurt along with muffins and breads, so that was okay. It was great to be able to keep our bags in a large storage area in the back of the hotel lobby until we left much later in the day for the last ferry. You certainly can't beat the convenience of the hotel right across from the Ferry Dock.
In general, however, I think the hotel owners are collecting money for the privilege of a "squat" on Block Island. I understand they probably make little money in the winter, and must "take advantage" of the summer tourists; but I find I must scold a hotel owner who doesn't invest in even the smallest bathroom improvements which would remove the "ick" factor.

This Inn is old, quirky, has its charms, and that is all fine....Just don't make customers pay a premium for what is NOT a premium accommodation.

I've stayed at another property last year owned by Block Island Reservations, The New Shoreham House which is less expensive but you have to share bathrooms. New Shoreham would have been fine if the other guests realized it was a shared bathroom situation as well and cleaned up after themselves. This year we decided that our own bathroom was def worth the extra cost to stay at the Harborside Inn. We rented room 224 which faces the back street (I can't recall the name of the street) overlooking the bicycle/ moped rental business. There's no A/C in this room and you don't normally need a/c on BI but our room was stuffy and remained so our entire time there. They do provide a fan and we tried putting the fan in front of the window to draw cooler air in, we tried facing it out the window to put the stuff air out and it never helped.
The room & our bathroom were very clean & neat. It's a great location, directly across the street from the Point Judith ferry. They include breakfast which is yogurt, fruit, muffins, toast, coffee, tea & juice. This year they expanded the luggage room which was a def improvement.

All this being said I think next year I'll venture out of town and try The Atlantic House or another inn/ B&B on the island.

Our room was extremely small. The bathroom vanity was located in the bedroom and the air conditioner was a free standing unit that took up a lot of room. The mattress was hard. The room and bathroom were clean and the linens were fresh and clean too. The soap provided was tiny so bring your own soap. The a/c worked well and so did the small tv. If you arrive on a ferry from Rhode Island you'll be across the street from the hotel when you arrive. If you take the Montauk, LI ferry you'll need to take a cab to the hotel. We paid $270 per night with a two night minimum. The rate also included a continental breakfast. There is no elevator or bell service so youll be carrying your own bags up the stairs. Overall, a lot of money for very little. I doubt we'll be going back.

Overall a nice hotel right in the middle of all the action. Decently clean and adequate for a two adults and a preschooler.

Some details:
We stayed in a 2 room "suite" at the harborside. It was a corner room, so the living area had two windows, the couch folded out to a queen bed. The bedroom also had a queen bed. The couch bed was a little uncomfortable, but fine for our three year old. Both rooms had TV's, which was nice for our family at night. The couch was white, and got dirty, but otherwise the room was clean. Bathroom was small, but has all you need.
There was no AC, but we brought a large box fan and a small fan with us from home and with the two fans provided, it was more then enough.
The breakfast provided was adequate. Bagels, muffins, danish, yogurt, some fruits, orange juice coffee and tea. Enough to get you started.
The building itself seems to not have settled well over the years, and the floors are very slanted! It didn't bother me in the room so much, as the building is old. But, the main stair case made me feel like a drunken sailor every time I used it. I made my usually capable 3 year old hold my hand every time. I would recommend the hotel look into leveling it out even a little bit.