I was here on recommendation from a tour agency and regretted it. There are a lot of superior hotels in the downtown area. This one should be avoided if possible. The room is old and smells some. The bed covers are old and the interior is tiny. The bathroom is especially cramped.
The room is rather dark with an old tv. The manager is quite impolite and unaccommodating. I was rather put-off by his poor manner of service. The staff appears to be very good but they are running scared of this manager guy. Hope you don't have to deal with him. He was as bad as the rooms.
The breakfast was fair and acceptable. I've had better at other hotels at the same ratings.
The best aspect is the hotel's location. It's right in Shinsabashi and near the shopping arcades. It's about 15 minutes walk to the Namba Train terminal and about 5 minutes away from the subway, easy to find. Also, they provide a free lan line for internet if you bring your own computer.
In terms of the traditional Japanese cleaniness you would expect to find in Japan, this hotel is not a representative example I think.

I stayed in Metro The 21 for 2 nights with a friend. We had a double room. The location is amazing for Osaka. Namba is the liveliest place in Osaka with lots of shops, restaurants, bars on so on. Metro The 21 is by the Dotombori river. The hotel and the room was pretty basic budget-hotel type, but if that is what you need (a cheap place close to the action) this is a good choice. A great plus was the breakfast included to the price. There were both Japanese and western choices in the buffet. In our thip this was the only hotel where breakfast included to the price, and it was very convenient indeed to get your day started without hunting for coffee and food. So this hotel was definitely good value and a great choice for a short stay in Osaka.