I stayed here for one night last week. Everything has already been said here. What stood out was the friendliness of all staff.
I have been pre-upgraded into a Deluxe room. As said above, identical room structure. The plus is, that it is on top floor and that floor runs only half the length of the building. Given there are less room, the likelihood of less noise from the hallway is quite high. Maybe we were lucky, we had all the piece we wanted and needed! The real drawback was the temperature which I could not lower much by thermostat. It was way too warm but cooler in the hallway.
They arranged for a huge Christmas party downstairs the same night. However, this did not affect us except that we had to pass by to the only lift that goes up to floor 5. I had to find out that the bar is behind the restaurant and when I remember correctly there was no sign for the bar from the lobby. A friendly employee who arranged for the Christmas party told me when I asked. And inspire of sending me to the bar for a coffee he offered me a cup of coffee from the machine standing in front of the meeting rooms where the party was going to be. A very nice gesture.
I am not so much in love with HGI and find them rather monotonous and dull with the dark furniture. Also, breakfast is not that great in my view. I know that many FTers vote differently here.
I did not try the restaurant for dinner. We walked to "Vivagusto" instead. That is an Italian restaurant and pizzeria sitting right on the other side of the busy main road. The hotel is in a short distance from that road so it is near by and easy to find. it is run by an Albanian guy (many pizza places in Switzerland are, meanwhile) who is absolutely welcoming and friendly. I would go there again.
As escape4 already pointed out, going from Dietikon (train station) via bus 303 until Racker stop (4th stop from Dietikon train station) is easy. I would prefer then Hilton Zurich Airport anytime because it offers more (Executive Lounge, Sauna and better breakfast). However, the HGI is a lot cheaper and does the job.