Well, most of my time was spent in Hokkaido, which is cold. Depending on what time of year you go it's going to determine a bit of what you're able to do and how you enjoy your time. Winter time was great for going to an onsen (hot spring) because nothing warms you up and relaxes you like one of those. In general though, I guess I'd say that it's a pretty clean place. There are a lot of parks and greenery most places you go, and the food is pretty great wherever you are. Even going to the 7-11 is fun because the quality of the food is way, way higher than anything you'd ever see in an American 7-11 (probably anywhere else you might find one) and in general you're in a food-lover's paradise so long as you like fish. Cheap sushi there is as good or better than expensive sushi you find elsewhere. (Actual Japanese people may disagree, but they're used to much higher standards.) People are really polite and helpful, and as a tourist you may get some deals on things you buy if you go to certain stores like Don Quijote. I think it's a great place to shop in general, because there are (or ought to be) a lot of used media stores so you can get lots of music cheap (as long as it's not super new) and manga, and if you find the right stores you can get figurines or plushies or whatever else.
The temples are pretty interesting. I got to go to Kyoto not that long ago and it's a pretty neat place, though I'm more of a big/modern city kind of person. Not that Kyoto isn't modern, because it is, they just have all those temples and things as well.
woooo that was very tl;dr