Lovely beachside. Perfect place to walk on their corniche. Nice small city. People r much friendlier than Merrakech. Not much scams by taxi drivers.

I recommend visiting Rose Valley just 1.5 hours drive from Agadir and if you have kids, crocodile park would be worthwhile visiting as a brief stop mine liked it. 

Marina apartments are next to beach and have swimming pools for both adults and children is a good place to stay. Alternatively, many hotels all within walking distance from beach. Enjoy the beach hire a chair for 20 dirhams for as long as you need and have mint tea at the beach. Agadir itself has not got much cultural heritage as compared to Marrakesh but it has a pleasant weather and relaxing holiday. Visit the street side fish market, where you can choose your fish and they will prepare it the way you like.

Visit the Agadir forte and take the cable car to the hill top. From Marina you can either take boat for yourself or get tickets for pirate ship trip. Pirate ship often puts loud music so double check with them.

Taghazoot is much calmer and tranquil holiday by the sea side. You can visit Taghazoot from Agadir as well. There is a local bus as well as you can take taxi. The bus from airport does not run all the time check the timings when you land. If it is not running you will need to take taxi. Around 100-200 dirham depending upon time your luck and bargaining skills. There is a crocodile park which probably is a disappointment I visited Agadir multiple times but gave it a pass enjoy the warmth of Moroccan hospitality it will be a good change from British cold weather wise.