A lot happened in "Slither," but I still feel like The Secret Circle is missing key ingredients. For one, we never really got to know Nick and Cassie didn't either. His death, while a big event, doesn't carry too much weight because he was just a guy in the circle. We saw some of his personality, but he never did anything of note (and for that matter, none of the other characters have either).
Another problem is that we see all the parties and what they're up to, and there's little mystery in terms of characters. We know exactly what Dawn and Charles are up to, and what the circle is doing. Aside from the twists at the end of each episode, there is little in the middle of the episodes that is actually surprising.
Now that Nick is dead, I hope this is a turning point for the show, to let go of the limitations of the first four episodes and tell a story without getting caught up in exposition about the past, most of which should have been drawn out through the course of the story.