Just had another excellent stay here last weekend. Friday to Monday.
Location: When staying here I take the Keisei Skyliner to Ueno and then the Hibiya Line to Roppongi station. Takes about 1.5 hours, but it's a nice option if you don't have large suitcases with you. It's exit 1C from the station, and about a 5-10-minute walk from exiting the station to the hotel. Just go up the escalator, turn right on the pathway and go into the mall. Hotel's entrance from here is clearly marked on the right. Just go down the escalator and enter the hotel from there. Bellhops will help you from there.
Roppongi Hills is a very upscale and nice area. The mall is very nice, and there is plenty to do in the immediate area. Roppongi station is not far from Shibuya, Shinjuku, Tokyo Tower, and Ginza. Just a few stations away from each, although Shibuya and Shinjuku require a transfer to the JR line. Not hard though.
Service: As you'd expect with a Grand Hyatt and being in Japan, service is amazing. At times it is so good it is borderline uncomfortable (many people bowing to you when entering/exiting The French Kitchen for example), but I won't complain about that! Every employee I interacted with was great, and a special shoutout to the concierge team. They are especially awesome.
Room: I was in a standard double room. The view was nice, the TV had a very good picture, the beds were comfortable (for me at least, I know opinions on beds in Asia differ), and the bathroom was of good size. Nice shower/tub area, a small TV to watch when showering or bathing, and of course a nice Toto toilet (in a separate room). Plenty of storage room for me as well. Overall it was a great room that was a good size for Tokyo, well-appointed, and clean and well maintained.
Spa/Gym/Pool: Very nice pool and gym area. The locker rooms are nice too, and you can rent what you need for the pool (caps, which they require to swim, goggles, and whatnot). I enjoyed swimming laps here, although keep in mind this is a shared spa so one lane is reserved for local users of the club. I did not use the spa, so can't comment on that. The gym is nice too, nice equipment.
Dining: This hotel is a dining location quite frankly. Tons of options, all of them great. Between my three stays here, I've tried all but two restaurants here. I won't go through them all, I'll just say all of them have great service and food. It's awesome. I do recommend Keyakizaka for lunch or dinner if you can. Fun experience and amazing food. Our chef spoke good English too and explained the dishes to us. It was a lot of fun. Try it if you can. Shunbou is great for dinner too. Finally, if you eat at The French Kitchen for breakfast, get the french toast and berry smoothie. You'll thank me later.
All in all, this is an awesome hotel. No, it's not the Ritz Carlton or Four Seasons Tokyo. But it is damn good, and I actually think right now I'd rather stay here than the PH Tokyo. Call me crazy, but I think the awesome dining options and better (IMO) location push it over the edge.