Great hotel, great location!
We stated here for 3 nights around July 4th, and really enjoyed it. The hotel was clean, modern, and the location was outstanding. Except for the price (>$250/nt) and the lack of restaurant choices, it was fantastic.
The room was fine, but no free wifi in the room, which is a small negative. There is wifi in the lobby, but sometimes you just want to chill in your room and surf the net (aka troll on Facebook or edit reviews on TripAdvisor). Loved the small fridge in the room, and the beds are always comfy at the Marriott. Easy check in and out, no complaints there. Nice view of Boston, but not a river view on this trip, oh well. The elevators were a bit slow, but nothing too annoying. 
The rest of the hotel was good. Nice gift shop with snacks and souvenirs. There's a starbucks in house, for you coffee drinkers, and the restaurant was fine if you enjoy sports bars. The pool was very nice, but a bit crowded.
The location however, was outstanding. Right next to the prudential center and just a short walk to the Back Bay sights. The river was close by and we hung out all day for the fireworks and festivities then walked back to the hotel. Not a bad walk and oodles of fun!
We're going back in September, and will definitely stay here again, as long as I can save up enough $$. :)