Mice
We couldn't check in until 9:00pm because the hotel's computer system was down. We had to come back to the front desk four times over several hours, and kept being told they couldn't tell us when check in would resume. Needless to say, this was a huge frustration after a long day of traveling. Moreover, our first night there, the hotel was under construction. There was earsplitting jack hammering in the lobby well into the evening. However, it seems to be complete now (or maybe they just stop on the weekend?) 
That said, they did upgrade our room on check in and offered free continental breakfasts for our stay. But the problems quickly resumed the next day. Several elevators were not working. At one point people became stuck in an elevator and were banging on the door to be rescued. There was a conference and a number of student groups at the hotel, compounding elevator and noise problems. 
The pinnacle of the Park Plaza experience came when a mouse wandered out from behind the heater in our room in the middle of the afternoon on our first full day there. We've stayed in a lot of cheap hotels and have never seen a rodent appear in the bedroom. From the reviews below, there is clearly an infestation (the problem doesn't seem to be surface cleanliness because the place didn't look dirty). After reporting the mouse, we were moved to a very nice large room on the other side of the hotel and didn't experience problems after that. 
Despite all of the above, it's not actually a terrible hotel. The staff were reasonably polite. The 15th floor "Towers" rooms were nice enough (I believe the rest of the hotel is not as well renovated). Luckily, we only paid $100/night through a booking website, so we weren't that upset with everything. If you can get a good deal and swing an upgrade to the Towers, the place is tolerable and the location is great. But if you're willing to pay a bit more, there are tons of better, presumably mice free establishments around.