While 10 hours is probably enough to get all the way into Tokyo and see a couple things I'd probably go for Narita town and the temple there instead. Way easier and less stressed of a stopover. You can pass a few hours there without too much trouble and still have some time for a shower and lounge hopping.

If you do go into town I'd probably try to catch things winding down at Tsukiji and then over to the Imperial Palace then walk or train to the Shibuya and Harajuku districts and then back out to the airport.