We've stayed in Daisuke's Green apt for 6 nights and we were so happy we chose this place for our Tokyo stay.
Daisuke was the best host we could wish for: before our arrival he helped us so much by providing lots of information about transportation, rental bikes, places to eat, drink, and he made us a reservation for a nice restaurant. During our stay (and even after we left) he kept in touch to make sure we were okay. We've stayed at many places in the world, but Daisuke really stood out as a host.
We also loved the apartment's location: Shimokitazawa is a nice neighborhood and if you're not just in Tokyo for the famous high lights, it's a really good place to stay. It's quiet at night and in the mornings (many places open around 11 and most people leave around 6) but very hipster/East London, during the afternoon. Shimokitazawa has lots of nice coffeebars, restaurants and shops and not too many tourists (yet). The apartment is only a few minutes walk from the station and the station is only 10 minutes away from (direct line) the hustle and bustle of Shinjuku. Notice that when you have a Narita airport flight, the easiest thing (when you don't want to transfer more then once) to do is to book the Narita Express from and to Shinjuku, which costs you about 30 euros pp, single. It will be a two hour trip. You might want to look into Haneda airport flights or using a JR railwaypass (especially when you're also planning to travel outside of Tokyo).
The apartment itself was great, too. For two persons it was perfect. Like every apartment in Tokyo it was small, but it had everything we needed (washing machine, good shower, a warm toilet seat ;-). The apartment was clean and the AC helped us getting warm at night within a few minutes. We opened the window every day during the day to get some fresh air, which was great (and also a little dusty, that's the downside of a big city like Tokyo). The best thing about the apartment was the bed. Most places only offer a 1.20 or 1.40 m bed, which would be cosy, but uncomfortable for 6 nights. After long walks during the day we had good nights of sleep, and we're thinking of buying a tempur matress at home now, too