The rooms are 'smallish' from a North American perspective but are pretty much on a par with what you'd get in NYC, London or Paris and less expensive. We had a room with breakfast, which we thought was pretty good. Did not notice any particular issue with the bedding; we slept well enough and it was quiet.
Shinjuku station is an easy five to ten minute walk from the hotel. Last time we were there, we flew into NRT and took Narita Express to Shinjuku. Making your way from HND to Shinjuku will require a transfer but ought not be a problem and is faster and less expensive.
Easy access to many sights using Shinjuku as a base.