Here's a bit about my experience of Marrakech...
Sightseeing: Wandering around the city and soaking up the atmosphere is one of the best experiences you can have in Marrakech. There are certain things you have to see - the souks (see below), the main square at Jemaa el-Fnaa, Jardin Majorelle, and there are various palaces you can visit (we went to the Bahia Palace, which is featured in some of the pictures above). If you stay in the medina, you'll probably find yourself in Jemaa el-Fnaa on a daily basis, and it's wonderful, with lots of music, dancing, street food, shops and stalls, and snake charmers etc (I got to hold a snake!) It's also a great idea to go up to one of the cafés that overlooks the square and watch the sun go down. But most of the time, I was happy just to wander around and see as much as I could of the place, people and culture. I suppose it will depend on the individual traveller and where you've been before, but for me, Marrakech was a TOTALLY different experience to any other holiday I've had (I've been to 7 European countries and New York) and it was exhilarating. Walking around the city, especially the older parts, you truly get the sense that you are sampling a completely different culture, and personally I found that to be the most interesting thing about the holiday. Even now I'm back, just thinking about it conjures up such a vivid, vibrant, colourful picture in my mind. Late May proved to be a good time to go: it was hot and sunny enough to sunbathe, but the heat wasn't unbearable and the shady streets were pleasantly cool and breezy.
Relaxing: We stayed in a riad, which (as I mentioned before) was in the medina, the old part of the city. There was a lot of activity and noise outside, but the interior of the riad was like an oasis of calm. It felt very private (I hardly saw or heard anything of the other guests) and it was incredibly relaxing to spend time there: I tended to spend the middle of the day reading on the roof terrace, and go out in the late morning and early evening. This helped the city experience from getting too overwhelming, and meant we opted to stay in the city for the duration of the holiday rather than taking daytrips to other parts of Morocco (although if I went again I would certainly do this). Obviously, I can't compare and contrast with a Marrakech hotel as this was the first time I've been to the city, but I was glad we stayed in a) a riad and b) the medina as it felt as if we were getting more of a flavour of the authentic Marrakech, and having a different experience from the usual generic hotel thing. Another advantage of the riad was that the staff were incredibly friendly and helpful - I genuinely felt that they were more than happy to do/arrange/help with anything we needed. I actually found this to be the case with the vast majority of people we met in Marrakech.
Souks: The souks are a city in themselves - you could go to Marrakech for a week and do nothing but explore them, and you still wouldn't have seen everything. There was SO MUCH that caught my eye, and I wish I'd bought more - in the end, I got a couple of pairs of trousers, a real silver and turquoise bangle, various cheap bracelets, a big bottle of argan oil, some orange flower perfume and a couple of solid fragrances, and a tea-light lamp. Actually, that looks like a lot of stuff when I see it written down, but there were many more things I wanted to get - handmade leather bags and shoes in particular. If I went again, I'd have more of a plan as to exactly what I wanted to buy, along with a budget... It's a good idea to have a strategy as the shopkeepers are amazing salesmen and you'll be walking off with a bag full of stuff before you even know what's happened! There's also a tempting selection of fake goods on offer and I couldn't resist picking up some very authentic-looking Ray-Bans for 30 dirham (just under £2.50).
Food: I don't eat meat so I was slightly concerned I wouldn't have many dishes to choose from, but I needn't have worried. Moroccan food is delicious and has a more sweet than spicy taste. Every restaurant serves countless variations of tagine and couscous dishes, and at one cafe I had an absolutely gorgeous pastilla filled with goat's cheese, pumpkin, leeks and orange. Something I loved about Moroccan food was the fact that everything is cooked with fruit - absolutely perfect if, like me, you have a sweet tooth! The breakfasts were amazing too: more than I could possibly have eaten, including piles of gorgeous pastries that were so much tastier than the ones you get over here. Of course, mint tea is served everywhere and it's delicious (and I say that as someone who doesn't like tea). It's made with fresh mint leaves and lots of sugar so it has a really fresh, sweet taste and is very refreshing, even though it's served hot. Food and drink is also very reasonably priced in the smaller restaurants and cafes.
Cats: CATS ARE EVERYWHERE - on the streets, around shops, lounging around inside the palaces and gardens, even in the hotels and restaurants! I suppose if you don't like them this might be an issue... But as a cat person, it was heaven. A lot of the cats are shy but some are really cheeky and will come up and try to get bits of food off you. There are also kittens all over the place. KITTENS.
Altogether, Marrakech was an amazing experience and one of the best holidays I've ever had. I'm already keen to go back and find myself daydreaming about the place on a regular basis: along with New York and Malta, it's been added to my list of travel destinations I completely fell in love with, and has made me desperate to travel to more non-European destinations asap. Definitely a city everyone should visit.