Even as a citizen of Rotterdam, I went visiting the Euromast Tower again last year and still enjoyed it. First you take a fast elevator which brings you in the restaurant on about 90m height, then you have the ability to walk around on the platform outside. After that you can go into the so called Euroscoop (glass elevator) that gives you a nice panorama sight of the city.
You only have to be lucky that it's a clear and maybe even sunny day, what makes the view much wider than on cloudy days.
There is a possibility to get something to eat and have a drink; in the restaurant on ground floor or the one upstairs. The Euromast also has two hotel rooms on the platform deck.
When you're more into thrills you can even book an arrangement to abseil from the tower!