This 243 meter high building has a viewing deck on both the North and South towers on the 45th floor which is at the height of 202 meters with wonderful panoramic views . I definitely can recommend visiting here as it’s free! It also has quite a nice gift shop.
On a clear day you can see Mount Fuji but it was quite hazy the day I went up. The North tower stays open later so you can have night time views.
Around the area of this part of Shinjuku, which is West and is known as the Skyscraper district there are more interesting buildings like the sompo Japan Nipponkoa Head office building headquarters for Sompo Japan Insurance .
Another is Mode Gakuen Cocoon Tower (very similar in design to Londons Gerkin I think) This is an educational facility home to three colleges.