Great value and good amenities! It was really nice having a washer with a giant tub of detergent, as well as a balcony with lots of hangers to get everything dry. The air conditioning was powerful and the bathroom (shower/tub room) was spacious and a delight after a long day. The bed was a little soft for our taste but we like a rock-hard mattress, so it's more an observation than a criticism.
One thing to keep in mind is that Hatagaya Station is on the Keio New Line subway line. It's only three stops from Shinjuku station but those stops are not covered by the Tokyo Metro pass that many visitors use. You can either buy a ¥130 ticket or use a Suica/IC card if you have one when you're heading from Hatagaya-eki to Shinjuku-eki; on your way back, you need to stop by the ticket office or ticket machine and pay a ¥130 fare adjustment if you use your pass to enter your departure station.
This was a small inconvenience but overall we liked Hatagaya, which was a real neighborhood. There's not as much right at your doorstep as you would have in Shinjuku or Shibuya, but it's super chill at night. Within short walking distance, Nejishiki (ねじ式) has good ramen and nice people at the counter. You order by vending machine, for which there is an English-language guide, but they don't speak much English themselves.