We booked a corner suite with a king-sized bed and the rounded windows overlooking the street. It was spacious, comfortable, clean, and had the view of the hustle and bustle along Collins Avenue. The room was surprisingly quiet, given the traffic and very busy restaurant just one floor below us, and the AC kept the room comfortable. The bed and bedding were very nice, and the bathroom had a giant tub as well as a shower with two shower heads.
We stayed for 5 nights. The Marlin is only a block from the beach and Ocean Drive, which was an easy walk we made a few times a day just to people watch and grab a snack or drink. Parking was a block away in the municipal parking garage, and it was very easy to get in and out when we wanted to drive somewhere.
The service was very friendly and helpful. There were only a couple things that were not perfect, and we have laughed about it - nothing serious. First, the TV in our room turned itself on intermittently the entire stay. I slept with the remote next to me, and would just turn the TV off if it woke me up. Second, we had a Nespresso machine in our room, but were only replenished with decaf pods. We even asked for more regular pods, and they brought us a whole bunch more decaf pods. I don't think the staff could tell the difference for some reason, but it was funny and they were trying very hard so we didn't say anything.
If you want to stay in a wonderful, historic, slightly quirky hotel in South Beach, we recommend the Marlin.