We stayed for 3 nights in the Artist House over New Year, and it was a delight.
The location is ideal, being handy for all the attractions of Key West but not so close as to be noisy (and this was New Year remember..) The building itself is lovely, full of character and beautifully decorated, and really reflects the obvious pride the owners and staff take in it.
We had the smallest room (the Sun Room). I had been warned it was small when making the booking, particularly the bathroom. There's no doubt it is small, but I'm 6" 2 and it wasn't a problem - I managed two showers a day!
Happy hour was great, (free drinks, what's not to like...) and a good way to meet other guests, all of whom were lovely company. We found the breakfast to be extremely good - plenty of choice, and very fresh.
We received plenty of help and advice from both Jo, the owner, and various staff, including helping us find a dinner booking for New Years' eve, and I have to say all the staff involved in running the Artist House could not have been more accommodating.
Some previous reviews have found criticism in things like the narrow wooden staircase up to the Sun room and the small bathroom, but frankly, if you really are that bothered by bathroom size and staircase width, as opposed to character, charm and friendliness you probably are better off in the Marriott.
For us, it was perfect.