The hotel is located right behind the Shinjuku's "Kabukicho" red-light district. The area is considered rather messy & complicated, with many bars & clubs, and of course more drunken people. And the hotel is located in the 'Love Hotel' area where you will see rooms available for 'hourly rental. The location is not great because it's rather 'hidden' from the main streets.
However, it also gives you good access to the JR or metro stations (be prepared with a 10-15 min walk), restaurants and department stores. And a 24 hour supermarket is located right across the corner of the hotel... with good selection of all sorts of Japanese wines & sake. The hotel building was renovated not long ago (maybe 3 years?) and so it's quite new. Internet access is free of charge in all rooms. And similar to most business hotels in Japan, the rooms are fairly small - but comfy and very reasonably priced.

This was the firts Hotel where I stayed during my stay in Japan.
It was amazing to feel that I was in such a vibrant neighborhood.
Great located, near the JR to go to the airport, to anywhere in the city.
Restaurants, clubs, stores, convenient stores, markets, supermarkets, Shopping malls, everything is just there!
The street is quite but it is where you want to be.
It has to be said though, that around are lots of bars for men, which could be quite intimidating for families or women. I did not mind about it and I did not feel agressed or unsafe or whatsoever.
The room was quite small but had everything you may want. Clean, with a traditional japanese bathroom, nice amenities. Perfect!
If I go back to Tokyo (Which I want to do soon), I would go back here. It was just so convenient!

My husband and I stayed here in March 2011, a few days after the earthquake. The hotel wasn't busy (we saw only 2 other guests in 5 days) The staff were very reassuring about the situation in Tokyo (the nuclear situation!), and allowed us to use the internet free to keep in touch with family back home. The rooms were very nice, the wet room great, and the breakfast arrived every morning within a few minutes of our calling for it. (Not always to our taste, but different and interesting!) Every night there were 3 or 4 aftershocks...the staff were unconcerned...we were pretty scared! Its in a great area of Tokyo...and I wouldnt hesitate to stay there again.

Booked this hotel based on the great comments here. It was my first time to travel to Japan, and I saw the popular reasonable priced hotel, from their pictures, they seemed old-fashioned and very small, so I was very hesitant.

The hotel is just a little bit hard to find, it's not as hard as other people say if you prepare well in advance, but it's not like it's on a main street or close to subway like some of the other hotels in Shinjuku.

During my trip I stayed in HVF Shinjuku & Sunroute Plaza Shinjuku, to give a better idea, here's the comparsion of both hotel

Location:
HVF: takes about 8-10 mins walk from the main railway, you'll have to pass through a few different small area to get to the hotel
Sunroute: it's right above the Keio line which is useful for me since I was taking the train back to the airport and I didn't have to walk far with my heavy luaggage, it's also only 1 and a half block away from the Shinjuku JR Station.

Room:
HVF: room is small with quite large bed, bed was comfortable, but since the large bed, there's not much room to do anything in the room. I have to give great compliments to the bathroom though, it's almost as big as the rest of the room. The toilet & the bathing area has a door to separate, so it's good if you're taking a long bath & someone has to use the bathroom. The bathing area has a bathtub and what was really great is there's a big shower area next to the bathtub, they gave this little chair to sit on while you're taking your shower, i think that's a nice experience of how Japanese lives and I didn't even want to go out of bathroom!

Sunroute: The room is small and the bed is small too, so there gives just a bit more room to move around. The room design is simple kinda like a business hotel, although the bathroom is old with the white walls turning yellow. It's not bad, but I'd prefer the room for HVF.

Others
HVF: It's a small boutique hotel, so don't expect it'll wow you, but it gives more than what a "real" hotel can offer you, they even offer free sandwiches for breakfast which taste awesome! If you don't mind the walk, it'll be a preferred choice as I believe the price is cheaper.

Sunroute: It's very convenient and great value for the hotel. Considering the price, it's newer and more comfortable than other hotels at the same price range.

Coming month, I'm going to Tokyo again, I choose to stay in HVF than Sunroute because it's a bit cheaper, and although the room is pretty much the same size, since the bed is bigger it gives me a more comfortable sleep.