I'm still really enjoying the series because it's hard to put down and I care about the characters now, but it really feels as if the first three were planned and then because they were a success they decided to publish the rest.
It's still dark, funny and deals with issues that normal YAs often skirt around, but it's a bit like reading an epilogue. I know it's now building up to a new villain, new grand plot, but... Maybe the next one will be better.