It's hard to find affordable rooms in HK now and Cosmic definitely has some good prices.
I have stayed there a few times and the rooms are variable, although definitely you get what you pay for. The cheapest rooms are very small and they are windowless, however they are very good value for money. They have better rooms available if you have a more generous budget to spend, and they are the ones you are more likely to see in the hotel advertising.
I see a lot of the reviews are quite negative, but I think people maybe expect too much. Space is at a premium in Hong Kong and you would expect to pay a lot more than a couple of hundred dollars (HK) to stay in a large room right on the Nathan road.
The hotel is at a good central location. The staff are generally helpful. The wifi is good (and free).
I would reccommend it to anyone visiting HK on a tight budget. There are plenty of other hotels housed within the same building, (Mirrador mansions) and I have been to quite a few of them, but this is probably one of the best and most reasonably priced of the ones I've stayed in.