Achivadolimni was the only beach we visited two times.
I warmly recommend it, although it may not have some colourful rocks or other unique feature.
The beach is huge, very huge, so there is space for everyone and you'll still be in peace.
It's clean, the sand is nice.
One part of the beach has facilities and the part closer to Adamas is peaceful, with nice rocks behind.
The seabed is very tame- sand, not one kilometer deep two steps from the coast.
The water was one of the warmest, clean and tame.
In front of you, you can see Plaka, right Adamas, and on the left nice hill composition (on three levels).