Apparently, I exceeded the space (text and photo) limit for the review and two sections got cut out, so I have posted those sections below:

Fitness Center/Spa/Pool

There is a fitness center at the hotel but is closed due the pandemic, so I did not get a look at it. There is no spa or pool at the hotel, but I was told that you could get an in-room massage, which is pretty standard at Japanese hotels.

Service

Because the hotel is small, service feels more personal than at larger hotels. However, since the hotel is new, my sense is that hotel staff are still learning and not as knowledgeable as they should be. Case in point: the person who showed us our room and explained its features could only explain in the most general terms and could not answer my specific questions. When showing us the tablet and how to control room features with it, I asked if it could control the opening and closing of the curtains and she didn’t know and suggested they could be controlled with the bedside controls, which they could not. Then she briefly explained how to use the electric piano and told us we could connect our iPhone to it via Bluetooth, but when I asked why we would want to do that, she couldn’t answer. Later, I discovered on my own that you need to connect to the electric piano via Bluetooth to access the room’s speakers to play music from your mobile phone. I also asked if there any tunes stored in the piano that could be automatically played back, but she couldn’t answer that either. After reading the piano instructions, I found out that there’s a library of 60 tunes, mostly classical, that the piano can play automatically by pressing a couple of keys. More simple things she could answer, and since she was very personable and friendly, these transgressions were somewhat forgivable to me, but these are things staff should know. Service in the restaurants and bar was exceptionally good and the staff was invariably friendly and ready to please. All staff wore baggy black outfits and black COVID masks. In Japan, hotel staff usually bow in various degrees of politeness from a deep bow, to a half bow, to a head nod depending on circumstances. But at this hotel, staff perform a trademark move that consists of placing their hand over their heart and then nodding their head or bowing slightly, which I guess is supposed to show even greater sincerity or heartfelt feeling than a normal bow. In my opinion, the Japanese bow in its various gradations is satisfactory, so this felt a bit gimmicky to me. Nevertheless, service at check-in, in the lobby lounge, club lounge, restaurant, and bar was very good, though I did get a sense that some people were perhaps a bit tired and overworked.

Overall

Mesm Tokyo reminds me a lot of the St. Regis Hotel in Osaka in that both are small, stylish, intimate boutique hotels with a luxurious feel. The main difference though is that the St. Regis Osaka is modern with a traditional bent, while Mesm is modern with a hipster bent. The room rates at both hotels are similar, even though Mesm is a category 6 and St. Regis a category 8 hotel, which may be fitting given that Tokyo hotel rates are higher than Osaka’s. Since Mesm is brand new, the buzz factor enables it to charge a higher rate at this time. Also, on the other side of Hamarikyu Gardens is the Conrad Hotel. Though I have never stayed there, I have seen hotel photos and it has similar if not better views of the gardens and the Sumida River and is a full-service hotel with spa, pool, several restaurants, and a club lounge. It’s room rates at this time of year are about 10,000 yen lower per night for a standard room (at a spacious 516 sqft) than at Mesm (430 sqft for a standard room).
Overall, I enjoyed our stay a great deal, especially the modern hotel design, the location and views, the friendly service, its smallness and intimacy, and club lounge with terrace. But in terms of value, I think Mesm is a bit expensive for paid stays, even compared to higher ranked hotels in Tokyo, so if money was a consideration, it would not be my first choice, but for point stays it is quite reasonable at 50,000 points or to use a free-night award from a credit card. However, with my travel patterns, its location in Hamamatsu-cho is an important consideration and I can see myself returning here again, but mostly for point/reward stays.