I stayed with my wife at Hotel G9 for 3 nights in July 2011. I have to divide my review into 2 parts:
1.) Positives
First and foremost location. Walking distance from anything interesting in Tallin including Old Town and Passenger Terminal (if you want to go to Stockholm or Helsinki).
The room itself was really basic, but you can count on clean bed and bathroom. If you don't mind student hostel feeling, you'll be fine.
Front desk was generally helpful in finding a safe parking space (details below).
2.) Negatives
Parking space is free, but unsafe and unsecure (it's a quote from the warning that can be found at the front desk). What it means is that there are occasional car windows breaking. Anyway it didn't feel safe to leave a car there. We spent quite some time looking for a good parking space and to save you the same trouble we recommend underground parking at the Rotermanni Kvartali. It is 10 minutes away and it has good 24 hours rate.
One other negative is aesthetics. It is not a nice building and you will be disappointed if you can't make an effort to close your eyes to some ugliness around and in the building.

This hotel is cheap: dirty and smelly entrance, two long flights of stairs to negotiate with luggage, very basic room that could use some new paint on the walls, tyny bathroom where water splashes all over. If you need to open a window, ask for a room on the back because the trams in the front are really, really noisy.
The location is quite good at five minutes from the old town but that is the only plus with this place which is more a hostel with private bathroom than a hotel.
We have used self serve hotels in Finland for similar prices but much higher quality.
Don't bother paying for the room breakfast - sandwich of white mushy bread with lots of butter and mayionnaise, non-dairy yogurt like thing, pretty bad coffee but this is cheap at 2 euros per person. I would certainly never to back to this place.

staed at this hotel for 5 nights close to old town and shopping centre /paid 30 euros per night for the two of us which was good value the room was large and clean// the staff were pleasant//could have been done with more coathangers and the stairwell could be done with a tidy up,but overall was quite pleased/// for a cheap meal try st patricks which do some cheap deals

Good location, free parking. Clean. Stuff is helpful, speaks foreign languages.