I stayed at the Rhiga Royal Hotel for 5 nights and can only recommend this hotel. The location might not be perfect (the hotel is located next to Waseda University), but in Tokyo location is not an issue: taxi fares are cheap, there is a metro stop nearby and the hotel offers a shuttle to one of the major train stations.
This hotel is not very popular with tourists and the 99% of the client base is Japanese which makes it even more interesting.
I have stayed in Hyatts, Sheratons and Hiltons in many different countries and can honestly say this hotel is up there with the best. The service is impeccable, the rooms spacious and the hotel offers a wide range of services (including a wedding chapel, photo studio and dental clinic :-)).
If you considering this hotel book online and select the super saver rate: 24.000 yen (excl. taxes) for a 50m² suite with a great view is pretty much unbeatable in Tokyo.
The hotel staff is very helpful but do take into account that is not a very international hotel so don't expect international TV channels.
In a nutshell, this hotel is gem to be discovered. The fact that this is the first comment on tripadvisor is the living proof.