Having stayed in Sleepzone many times a couple of years ago, I was looking forward to my stay again. On arrival, after checking in and leaving a ten euro security deposit, we were told that we were staying in a house across the street from sleepzone. The house was nice and clean and so was the room but the beds were absolutely terrible. They squeked so much that the two of us were awake half the night. As others have said the streetnoise is terrible too. You can hear everyone walking past. The fuse thing is also very annoying,especially as you are sharing a house with people, asking them to stop boiling the kettle so you can have a shower is a bit inconvinient. We decided to end our two night stay and only stay for the one night as we were just a bit unhappy.
Pros
Clean
The staff are very friendly and helpful
Good security as long as you were in the main building
Free internet access
Breakfast-although we werent there in time
The €3.50 car park down the road

Cons
I would have felt a bit worried had it been two girls staying in the house. There is no security at the house that we were staying so you dont know who you're staying with and unlike the main building you werent able to run down to the security guard
The beds are so noisy that you cannot get a good sleep
The street noise
Not being told about the security deposit until arrival
€10 deposit per towel is also a bit steep

We have always stayed in private rooms and they were always in the main building before and were a bit more comfortable so Im not sure why they changed it

The hostel was very clean and very central which was good. However, there were lots of 'hidden' extras. We were a group of 5 and it wasn't until we booked in that we were told we had to pay a deposit for each key, a deposit for the towels (which I suppose isn't that unusal for a hostel) and a security deposit per person.

All this is fine in theory, however we were not told this when booking rather when we were checking in. Also we were told that the security deposit (25 Euro per person) would only be taken as a pre-auth off the card and 'cancelled' after 48 hours. This was not the case - it was taken off the card and then put back after we checked out, causing us to loose £5 in the transaction.

The staff were friendly - didn't make it in time for the free breakfast.

We had a pleasant stay here in a twin bed room. The non-shared rooms are separate from the main hostel building, across the street in cute little renovated townhouses. Since the renovation is very recent, the full shared kitchen (there's one in each townhome) and property are nearly new and pleasantly modern. The room was spacious and sunny and the beds comfy with their own comforters/sheets/pillows included. The showers were kind of strange (very noisy from some electric generator that heats the water and you're warned not to use them when the kitchen downstairs is in use because a fuse might blow) although clean and convenient. Just remember it's a hostel so you have to bring all toiletries and towels (although you can get towels/hairdryer if you leave a huge deposit at the front desk). There's a barebones continental breakfast also available in the main building.

The location is very convenient, on a seemingly quiet street just off the main downtown area and right near a major shopping center with Marks and Spencer supermarket and more, so getting food for the kitchen is a breeze. Remember the whole town is really tiny, safe and walkable, so don't listen to the reviews that make it sound like it's far out of the way. Unfortunately the street doesn't stay quiet late at night as young drunken revelers return from the bars. If you can request an off street room you should; unforunately I never got a good night's sleep in Galway from all the partying students in the street. Also the rooms are thin in the house itself, and the loud showers, and the impossible to open main door lock (which you'd hear people struggling with at all hours) added to noise levels.

Overall great for the money, clean and modern, but try to get an off street room if you want an actual "sleepzone."

We booked a twin room at Sleepzone through hostels, and due to availability were allocated one with a shared bathroom. So we were pleasantly surprised on arrival to get a room in a terraced house across the road, with it's own spacious bathroom (Shower only, mind!) and a shiny new shared kitchen and sitting room.
The room itself was bright and pretty clean with lots of drawers and a wardrobe. One minor complaint would be the squeaky bed frames (you could wake yourself up by just turning over in the night!), but on the second night we put the matresses on the floor and got a quieter nights sleep.
Someone else has already mentioned the shower/appliances fuse issue in these houses, so I won't go into it here - bizarre!
We were at the front of the house, and the road outside got pretty noisy from traffic during the day, but as we were only in Galway for two days we weren't in the room much. The location is 5 minutes walk from the centre of Galway, so is very convenient.
Bit of advice for car drivers, do not park in the multi storey car park directly up the street from the hostel, it costs about 25 euro per day! There is a cheap outdoor car park at the bottom of the street (past the traffic lights) which cost 3.50 euro for the day, and free overnight. As long as you get down before 8.30 in the morning to put on a new ticket, it works out far cheaper. Thanks to the staff on hostel reception for this, as we wouldn't have found it!
Hostel iteslf has free internet access, and a useful luggage store room and lockers in case your room isn't ready yet. We didn't go to breakfast, but looked pretty basic stuff (toast, juice) - but hey, what would you expect in a hostel?
Staff were great and always helpful and available. We would definitely use this hostel again, it would be fantastic if you could get a party of 6 people in the same house!
One last thing, Sleepzone have a hostel in Connemara (west of Galway) with a shuttle bus between the two sights. If you can, go to Connemara, it's beautiful...