Our Krasnapolsky Horror Story
We stayed at the Krasnapolsky about three years ago. We had booked a non-smoking room, but ended up in a room that stank of stale smoke. We complained, and after initially being told that there were no other rooms available we were, eventually, offered an upgrade to what they called an apartment.
To get to this apartment we had to walk out of the back of the main building, walk about 100 yards along a canal (we only realised later that this was the Red Light District) and then let ourselves into a separate apartment block - it looked like these were probably once residential apartments.
Our apartment overlooked a very small inner courtyard - meaning no sunshine and very little light -, and it had a distinct musty smell. The furniture was ancient, and the whole place had a really dark, depressing feel to it.
The rooms in the main building are OK (it was just unfortunate that ours stank of smoke), but the apartment was just horrible.
So... you should be OK as long as you're in the main building and they get your smoking preferences right. Don't, whatever you do, accept an "upgrade" to the apartment block round the back!