If you are coming from the states, and taking a train, be sure to ask a person at the ticket booth for help purchasing tickets. The machines really don't like US credit cards.
Concourse D is a bit old and unfriendly. Would advise to stay after the passeport control area and enjoy the lot of places to stay before going to your gate.
There's a nice smoking area inside the airport in case you are going just as transit. If you got more hours, there's a museum inside too¡ Staff is very, very nice.
In case you need to check your connection flight after you land here, there are no flight boards. Look instead for rows of machines where you can scan your ticket and find out your gate number.
KLM "automated" bag check is the slowest & most agonizing I've ever experienced. Allow even more time than you normally would since you get funneled through it even if you checked in online