I stayed at the Royal Park hotel whilst on a business trip because it was close to my office. Needless to say, its proximity was not worth it. The property should be avoided.
Above all, the worst thing about this hotel is the air conditioning (if you can even call it that). I had it set to the lowest possible temperature and it was still hot - there is no way to control the fan's speed as well. If there was such a thing as an "extra low" setting, this was the unit was set to. I couldn't sleep at night and they didn't even have a fan to give me. Furthermore, the window doesn't open (not that this would help much). This can be unbearable in the heat of Tokyo's summer (33+).
There were other issues as well. I was booked into a room with a double bed and they tried to tell me that I actually booked a room with two single beds. I had to argue with the front desk staff and have my travel company call them (because I didn't have a confirmation printed out, which they insisted I provide them).
Eventually, I decided to switch hotels. I told them I was checking out early and, again, they put up a fuss by saying that I couldn't! I told them my rate allowed me to do so and, after getting into a lengthy discussion with the manager, I was finally allowed to leave. I moved to the ANA Intercontinental, which is a FAR better property and even had a lower corporate rate (at that point, I didn't care that I would have a 27 min commute to my office).
Some other thoughts:
Location - It is easily accessible via an attached metro station and a bus terminal with direct links to Narita. There isn't much else in the area except for a few restaurants, many of which are closed on the weekends, and mini-marts. There is a Starbucks about 10 min walk away. There are great areas of Tokyo, but this one doesn't showcase the city well.
Service - Per my above complaints, I wasn't that impressed with the service. The staff's English was okay to poor.
Food - I ordered room service once. It wasn't good and I never tried it again.
Rooms / property - They are small and clean. What you would expect from a 3 star hotel. Oddly enough, your key into the room is a skelton key. It may sound quaint, but I found it annoying to carry around. In general, the best way to describe the property is that it looks like something out of the early 90s.
Other points - The Internet is free (wireless and wired) and works well.
I am sure you won't be surprised that I won't stay at this hotel again. Tokyo is a great place, with many different properties to stay at. I don't see any reason why this one should be considered. I travel a lot for business and I can't understand why there are so many good reviews.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.