I had the opportunity to stay at this hotel for over three months consecutively. I don't speak Polish, but got along fine. The entire staff speaks English at a generally good level.
I stayed in three different styles of rooms. The regular room is not that impressive, but there's nothing wrong with it either. A little older, but standard to any older hotel. Their executive room is the best, in my opinion, it's well worth the upgrade. These two rooms are not much different in size, however, the executive room has a remolded bathroom that is just leeps and bounds over any of the other rooms below or above in price. The two room suite is nice if you need a lot of space and the bathroom is equivalent in size to the executive room, but it's not updated. The views from all the rooms I stayed were excellent. The preferred views are on the river side, because you have a whole view of the Vistula, Old Town and the Palace of Culture (big tower building with the clock). All the beds were very comfy. I am a huge fan of comfy beds ~ you are there to sleep!
The maids are excellent. Turn down service, fold your clothes, always very efficient. You receive little chocolates on your pillows. If you are able to go to the Executive lounge for evening snacks, you will find one of the best views of Warsaw. The ladies who serve the evening appetizers are stellar.
I recommend the breakfast and the italian restaurant within the hotel, both are a little pricey, but you won't find better food nor such a variety as the breakfast. If you need a break from traditional Polish cuisine, there is an excellent Mexican food restaurant a few blocks away from the hotel called "The Tortilla Factory". I recommend a Long Island Iced Tea, while you choose your favorite dish. For all three places, all their food is great.
All the staff were tremendously helpful and friendly. Just ask politely and they'll bend over backwards to take care of you.
One of the greatest advantages of staying at this hotel for travelers is the convenience of being RIGHT across the street from the trolly system (inner city travel), the national train system (travel all over Poland and Europe from here (Krakow, Gdansk, Berlin, etc), the underground Metro is very close and the buses are all over the place. The hotel staff will charge you a slight bit more to book your tickets for you (on the train), but you won't have to deal with the hassle of waiting in line and fumbling through Polish language to book your tickets. I used the hotel twice and booked the rest myself.
The city of Warsaw felt very safe to me. I walked all over the city at all hours of the day and night. I never felt threatened once.
I've stayed at a lot of hotels at all ranges of price and I had a truely great experience at this hotel. I checked out many of the other hotels in the area and the Warsaw Marriott is definately the only hotel I would stay. In fact, the only other hotel in Poland I would consider is the Grand Hotel in Sopot, but that's waaaay north and on the beach :>