Issues with Russian airspace.
As a few have alluded to, it's metric. Also, they use QFE for heights below either FL1800 metres or FL1500 metres. Don't expect any "altitudes" as it's either "standard" (ie QNH 1013) or "height" (QFE).
You'll fly what you filed. However, if going into Vnukovo (UUWW) expect at least a 90 deg cut onto the ILS so slow down early. Domodedovo and Sheremetyevo aren't as bad but it's better to be slow and one stage of flap out (or 2 depending) to make the intercept. Note if the approach controller is a PAR as well. A lot more chatter on the radio so be aware of it.
Runways aren't smooth at all! Esp if there's snow and ice on it.
Departures can be entertaining. Again you'll fly what you've filed. It's best to have your speed well under control and your vertical speed under control too. A lot of "stop climb now" happens in Moscow.
Winter ops need considering, cold wx corrections as well. Fortunately, it's fairly flat around Moscow. You'll probably need a gen dec or two to keep customs happy and if overnighting, you'll definitely need a visa.
Dry tables.
Is the runway grooved or other wise treated to allow dry numbers? Other wise it's wet numbers.