I had a really tough time accurately ranking the Inn at Glencairn. I was looking for a nice, quiet, comfortable spot convenient to Princeton for a weekend getaway for my spouse's birthday. We did get that. We were also treated to very friendly and accommodating service by the Innkeepers (Jon and Suzanne). The location is quiet, the Inn is a very old colonial era stone house that has been converted to a B&B. For the price (~$200/night) the Inn is nice and reasonably priced for what it is. And I suppose the most important aspect of the B&B (for me anyway) is the first "B" -- and the Bed was quite comfortable. Before I sound overly critical below, I want to be clear that I would recommend this place, but want to give an accurate description of what it is -- which I think, in a way, can be lost in the numerous 5-star reviews on TripAdvisor. This may well be a 5-star place w/ respect to the friendly innkeepers, but it is by no means a 5-star location w/ respect to its facilities, or its food. In those respects, it is 3-stars at best. But I gave it a 4-star review, because it is a nice location with nice owners who will treat you in a friendly and respectful manner.
The house itself, is very old, and parts of it date back to the 1600s. While it certainly has a quaint and authentic feel, it is not exactly fully renovated to the point that it could be. So expect creaky stairs, seeing through some floor-boards to the level below, etc., etc. Some might like this, some might not. The room we stayed in was fairly spartan (perhaps in keeping with the early colonial feel), but the bathroom was very barebones. (E.g., trash can from Target, uncovered box of tissues sitting on the back of the toilet, etc.) The bathrooms look circa 1980s renovated. Certainly not inviting or luxurious - but perfectly clean and functional.
I wanted the darkest and quietest room we could get, because my spouse is a sensitive sleeper. Jon was very accommodating on the phone, and said he'd put us in the back of the house, away from the (low-traveled) road, and in a dark room. It was fine -- but one of my big pet peeves was present: basically, no functional blinds. There were translucent curtains. We had to hang a blanket over the curtain rod. There appeared to be actual functioning wooden shutters outside the windows, but they were covered with spider webs, leaves, etc., and looked like they hadn't been moved in years -- and the window didn't look like it had been opened in years. So we left well-enough alone.
We have stayed in other very old houses that have been converted into B&Bs, but I guess the conversions were more recent and more significant overhauls Of course, in those cases (where the bathrooms, for example, were spa-like and high-end, with things like new clawfoot tubs, inviting shower spaces, candles, etc., etc.), the cost per night was higher (say $3-350/night). So again, for the price, this place is worth it -- but understand that this is not a luxurious house, it is a functional one (with a comfy bed!)
Likewise, breakfast was tasty and adequate, but no-frills: we got a waffle with one sliced strawberry on top. And coffee. Presentation, at a minimum, could be much-improved. No eggs, no bacon, no ham, etc. There may have been muffins, but I don't recall. We *were* treated to a very tasty home-made yogurt smoothie upon coming into breakfast, which was nice and appreciated. So well-meaning constructive criticism to the Innkeepers if they read this: dress up the breakfast a little - you can do it on the cheap. A small glass bowl of fruit with the waffle, for example, with a dollop of whipped cream. Some artisanal breads, cheeses, etc., at the table, maybe a big bowl of mixed fruit. Easy, right? And it adds a more high-end touch. (Also one of the Innkeepers came into the breakfast room at one point, and poured a cup of coffee for himself from the pot on the table - tacky? homey? You decide).
The Innkeepers also made a little cake for my spouse's birthday and sang happy birthday, which was quite nice, and truly appreciated.
I hope the above it helpful to anyone looking for a spot to rest their head near Princeton! I'd recommend this place, for the money, and given its quiet and slightly out of the way (but convenient) location, I think it beats out others that are either more expensive or louder.