Next House is absolutely huge, definitely the biggest hostel I've stayed at. It has a huge range of facilitirs, multiple bars and a restaurant. It's very social, and the hostel hosts a lot of events and does a good job of linking up solo travllers. Having said this, the flashy look of the place hides some of the biggest frustrations with this hostel.
The 4 person dorms are tiny - lockers dont fit a suitcase of any kind, and the hostel expects you to pay for suitcase/backpack sized lockers in the basement.
The ensuite is too small for 4 people to share, and would quickly get dirty and wet, particularly as the shower would leak onto what little of the bathroom floor there is. There was no storage, and very little hanging space, so it made having a shower and getting changed quite a chore.
The pod style bunks, whilst private, were hot and stuffy, even with the air con up to the max setting. If you have mobility issues I would reconsider booking this hostel as the top bunks are very difficult to get up to.
Finally, if you'd like to use the hostel Kitchen, you are forced to pay for the privilege.
It was also a requirement to pay for the gym and sports pitch, which are more understandable given they are above and beyond normal facilities, but for using a kitchen this seemed steep. I think this hostel sucks you in with the buzz of the facilities but lets you down on the dorms themselves.