I honestly found the first two episodes to be great.
First episode:
The first episode was fast paced which did lead to some scenes having to be changed, however with the limited amount of time they have they still did their best to include scenes.
Characters: I really enjoyed most of the casting, mainly Percy and Grover but Luke and Annabeth both did a great job playing their roles. It doesn't matter to me so much as what they look like because I found they all became the characters they needed to be.
Second episode: I really enjoyed how they took the time to show how Percy really saw Luke as a friend and how he helped him try to find what he's good at. The bathroom scene was good and the part where the spear is broken was done really well. I wish that the part where he is claimed looked better however they actually included it along side Chirons speech.
In all I feel like it was a good adaptation of a great series, with some differences it still feels like the series I've grown to love.