"Have a nice summer!"
Bringing her into the fold and making her an official part of the "Scooby Gang"* was always Joss's plan, but if that was the case then maybe he and the other writers should have given more thought to what she could actually do with her before they were ready to "activate" her as a character. Angel went through a similar problem, as I remarked in my review of "Never Kill a Boy on the First Date", but that was dealt with four episodes ago, and he's only a recurring guest character at this point.
*(For those newbies unfamiliar with the term, "Scooby Gang" was a term used in the writers room during the first season to refer to Buffy, Giles, Willow, and Xander. During season two, the term got worked into a line of Xander's dialogue as an inside joke, and eventually it became common for the characters to refer to themselves as "the Scoobies".)
Still, even though Charisma Carpenter's not the strongest actor of the cast, she does reasonably well with giving us a slightly more sympathetic side of Cordelia here, and the writers do a good job of respecting the original intent of the character (as a reminder of what Buffy once was, but can no longer be). but striking out in another direction.
The ending of the episode, with Marcie seems like it ought to amount to something later on, but it doesn't. Unlike most of the other instances of this so far this season, it's a shame this time, as I'd love to have seen more about these invisible assassins. Ah well.