Lots of great advice above. I think if you are certain you'll return, stick to Tokyo as your home base and research lots of daytrip options (or an overnight in Hakone) for a change of scenery from the Tokyo Megalopolis. If you end up changing lodging at some point, I'd strongly consider staying at a ryokan (Japanese-style inn) at some point for a cultural experience. Depending on your timing in October you might have great opportunities for fall foliage so do some research on that.

I just returned from Japan for a one-week trip. Did Nagoya-Osaka-Tokyo (we should have done Osaka-Nagoya-Tokyo for location logistics, but we added Osaka last minute and couldn't change our flight routing). What do you LIKE to do? Nagoya/Osaka/Kyoto is a lot of walking and sightseeing of temples and castles. After my 3rd castle, I was a bit castled out (because they kind of all look similar) - and for some reason, I thought they would have preserved the rooms and furnishings inside the castle but they don't. They've turned the castles into museums with displays for art, history, and other things - which is interesting, but not what I was expecting. We skipped a daytrip to Kyoto because it would have been more temples and castles - and I was tired from all the walking. I think choosing one location (Osaka or Kyoto) would be plenty and explore for 2-3 days rather than doing daytrips to each place. Then spend the rest of your time in Tokyo. Basing out of Tokyo and commuting back and forth is not recommended - you'd lose a lot of time that way.

That said, my favorite spot was Osaka. It had a great blend of old and new. And the InterContinental Osaka is amazing. Tokyo was very busy and we couldn't get dinner reservations to any of our top restaurants (even on weeknights).

We have very little interest in temples, castles, musems etc. That being said, we are going to Japan, and would certainly enjoy a day or two of exploring some of "older" Japan, and the parks/temples would be of most interest to us. But we won't be heartbroken to miss it, and I'm not sure it's worth the 50-60K yen to spend a few days there. In terms of restaurants, we are planning on finding back alley, hole in the wall, local jaunts, like we enjoy in most foreign cities. We will have no problem exploring various neighbourhoods of Tokyo, with no real plan - simply getting lost is half of the fun. That being said, 7 days is a long time so we will likely do some of the day trips suggested in this thread as well.

Too late now but the reason for your disappointment was that you chose absolutely the wrong cities to see castles. Nagoya and Osaka castles are modern reconstructions of the originals, with elevators, ferro-concrete construction and all the trappings of modern tourism - more like Disney castles than the real thing. Nijo Castle in Kyoto is pretty much original even though it is more palace than castle. So are Himeji and Hikone Castles. There are a lot of almost original feudal-era castles in Japan, just not in Tokyo, Osaka or Nagoya.

Thanks for that info! Will keep in mind for next time.