Unkept, sad garden. Shinjuku Gyoen is better
The Hama Rikyu Garden appears to have been a beautiful garden at one time. However, as of June 2006, there are currently renovations underway. Even with these renovations, the park does not measure up to Shinjuku Gyoen.
Traveling from the Shiodome subway station, we noticed that the waterways near the garden were polluted. Entrance fee was 320 yen (compared to 200 yen for Shinjuku Gyoen).
The dirt paths within the garden are muddy and one of the water ponds was drained due to the renovations. The park is surrounded by high-rise buildings. At the time we visited, there was also a very loud helicopter overhead.
The best part of the park was the waterbus stop. For 720 yen, you can take the waterbus from Hama Rikyu garden to Asakusa. The waterbus ride has views of 12 unique bridges (13 if you count the Rainbow bridge).
If you see only one garden in Tokyo, I would suggest Shinjuku Gyoen. While the waterbus ride from Hama Rikyu to Asakusa is a fun trip, the uncleaniness and lack of tranquility spoil Hama Rikyu garden.