Very spacious "beach"/plateau. There are a lot of stairs into the water, but do mind the sea urchins! I can't stress this enough! Especially when the sea is a little rough and you can't really see the bottom.
The water is very clear though and is really refreshing on a hot day, with enough restaurants and cafes in the area.
Beach with great history. Suitable for families with small kids. This is central beach in Opatija. Has couple cafes and restaurants but are quite expensive. In mid season is very crowded but there is always somewhere to put towel on :) Definitely place to visit and take a swim.
Slatina beach is old and it should be modernized. It is ok if you don't care...but there are so many other beaches which you should explore. For example the beach Lido is now part of the beach resort Bevanda and it looks great, than amazing Kantrida in Rijeka with modern pools complex, Medveja, Moscenicka Draga, Icici,...if you walk "lungo mare"...
The central beach in Opatija has nothing to offer but expensive service and concrete beach. In the high season it is usually crowded with hotel guests. On the upside there are a lot of good restaurants and bars around it. The parking is not easy to find!