Good advice above. To add my own...
You will find Morocco both exotic/adventuresome, but also a lot more heavily touristed than you probably expect - it's a cheap sun and beach destination for northern Europeans. So it's got a lot better tourist infrastructure than you might expect (at least in the popular areas). Trains are quite good.
Most interesting cities (IMHO): Marrakech & Fes. Meknes also good. Essouaria - mixed - it's a delightful location (on the coast) so is (literally) a breath of fresh air, but has become quite a bit touristy as it is now very popular with the sun-and-sand set (and cheap package tours from northern Europe. Least interesting: any of the ferry ports on the north coast, and Casablanca (the movie was filmed in LA, anything like "Ricks" is newly constructed for tourists). Connect Marrakech and Fes by train (a long day, but easy and comfortable - trains are a legacy of the French colonial days).
With just 5 days, you don't have much time for excursions - I'd split it between Marrakech and Fes, save the coast, mountains and desert for another trip. It'll help if you can speak a little French - it's everyone's second language (they speak it badly, so your bad French won't be mocked as it might in Paris).
Consider flying in to Marrakech and out of Fes - don't double back just to fly out of Marrakech. There are crazy-cheap flights to both from multiple cities in Europe. Last time I was there, we were in Spain and our return flight to the US departed from Paris. We used Morocco as our connection: flew from Madrid to Marrakech (took the train to Fes), then flew out from Fes to Paris. Flights were dirt cheap, it worked out perfectly.
Morocco is awesome. Have fun.