Shinsekai area does not have a great reputation but we were not deterred by it. We went there at night and I didn't feel any danger (mostly because my bf was there and Keiko)...I don't think going alone there is a great idea especially at night.
We walked around there at night to have kushikatsu and drinks. It's a very lively area. We saw a lot of drunk people walking around. And we saw a man falling off his bike because he was too drunk. He was fine though.
We even found a sake vending machine. I guess, they really like their alcohol. I personally liked all the bright lights, looking at the Tsutenkaku Tower, and the liveliness of the area. This area has it's own unique charm.