With that amount of time, it *could* be enough for a quick trip into Narita town, a quick hop by train. It's actually a very nice place to send the afternoon. Have a nice lunch at one of the many cute restaurants lining the main street. Then have an hours stroll around the very beautiful and famous Narita-san temple and gardens.
If that's feeling too ambitious for you, there are things to do outside of security if you don't want to spend the whole time in the lounge. A pretty comprehensive mall like shopping area on the upper level, lots of souvenirs and Japanese goods to take home, restaurants. For me, get a piping hot pork tonkatsu bento box (or sushi), some mochi/ ice cream and head to the nice and large observation deck. That's kind of nirvana like for me... if it sounds at all interesting to you, check it out.