Great property located at the FRA airport. You don't have to leave the airport to arrive. I wish there was a little more signage for finding the hotel inside the airport terminal, but that is not the problem of the hotel. The room was incredibly clean, the staff were very professional, the restaurant was efficient and good. Overall, this was a very convenient and pleasant experience.
I have a couple notes for travelers. First, if you're coming in late at night the airport mall will be mostly closed. Your primary dining options are simply to eat at the hotel restaurant. It is more expensive, but that's the price you pay for the convenience. The food isn't authentic Germany food by any means, but it will be fine in a pinch.
If you're going into town or coming to the hotel from the train, the hotel is directly above the train station entrance/exit. You will simply look for the elevators/escalators and go up a couple floors.
There are cheaper options, but none that are more convenient. The standards for Marriott are high and this property meets them all. So, you don't have to feel like you are sacrificing quality for convenience.
If you are carrying a lot of luggage, your transport to the hotel might be a little difficult. I'm not sure you can get where you want to go using a luggage cart.
Overall, when passing through FRA and needing an overnight at the airport because of either an early or late departure, this would be my top choice.