Pretty decent experience overall. Had the chance to chat with a few people in the lobby, but the atmosphere was quieter than I expected (this could be a good or bad thing for you). There was no happy hour at the bar, elevator was broken, no fridge in private room, no air conditioning (as described), no decent quick snack at the reception (although there is some grocery stores in a 5 minutes walk from the hostel). If you're looking for a private room just pick an hotel instead; though it wasn't a bad stay if this is the only option on a last minute trip then go for it, Berlin is awesome!