With English descriptions at the beginning of each group of displays, the English speaking visitor gets a rough idea of what it's all about, but no detail. Some of the displays look interesting, but without the information available in English it's vaguely dissatisfying. The brochure I received on entering had general descriptions of the displays on each floor in English but, once again, no detail.
The museum is in a lovely old building, with excellent, spacious display spaces and a varied collection of artefacts, models and documents. It's easy to find, using the map provided by the Tourist Information Centre right outside Sakuragicho train station. The museum is a 10 minute walk from the station. The museum is inexpensive at 300 yen and has lockers (100 yen, returned at the end). It also has a small cafe.
With so much else for a foreign tourist to do in Yokohama, I would recommend the museum to visitors who are in Yokohama for more than a week. There are so many other, better, attractions to visit. Even for history buffs like me, the museum is not that great if you don't read Japanese.