Not sure what information about "terrible stays" you're referring to.

I've stayed at the Marriott in Warsaw quite a few times over the past two years as a Platinum (although not in the last six months) and always had excellent stays.

I was given a corner room on each occasion, with great view and wonderful Plat welcome gift (I ask for nuts and red wine, usually).

Only drawbacks I found were (a) traffic in the area is rather thick at certain hours, in part because the Central train station is right across Jerusalem street from the hotel; (b) Prices in the 40th floor lounge were a bit high (pun not intended); and (c) the sports bar is a bit hard to find unless you know where you're going.

ADDED: By now you'll have been in Warsaw. If you stayed at the Marriott, I'd be interested in your assessment of the property and service. Did you feel you had a "terrible stay"?