Depends on the location. Generally it's not bad in terms of personal safety. But your unit might not have any amenities that make day-to-day living more comfortable. For instance, some cheap places don't offer air conditioners or heaters, space for a proper kitchen (only for a half-height fridge and 1 single stove), old flooring or walls (eg: rotting wood). Some places might not have a spot for a washing machine. And in urban areas, some tiny places might not even include a bathtub or shower (you have to go to public bath houses everyday).
well that has left me gob-smacked, I thought everywhere in Japan was hi-tech and modern, I suppose it like everywhere else, there is always old buildings ready to be demolished, thank you for the insight