The Terminal Hotel is a great choice for people that want a minimum of comfort in a central location. Rooms have their own bath and are generally clean, with few cockroaches only. It is also a very calm loaction - as long as you request a quiet room that does not neighbour the noisy street or the nearby night club.
The nice concierge might help you find reasonably priced safaris, excursions and overland buses - e.g. a minibus transfer to Arusha for 1300Sh (western tourists are often paying the double). If you are a single male staying in the hotel, you should be aware of the many young women that will try to make friends with you on the street and in the bars next to the hotel, and will turn out to be prostitutes.