I liked it. I thought Willow's POV scenes were nicely done, and at time kind of eerie. I'm a little confused as to the exact nature of the "spell" though. Am I to understand that in the scene with Anya at the end she was simultaneously visible and tangible to Anya and Gnarl but invisible and intangible to Buffy and Xander? Willow must have changed her last name to Schrödinger.
Re the airport scene at the beginning: it looked to me like the Scoobs were on the yon side of a security checkpoint. Yeah, granted it was probably a littler too close to the gate to be realistic, but at a small airport like Sunnydale it's not inconceivable. I was at Long Beach Airport this summer, and the security checkpoint was not much further away from the gates than was seen in STSP.
Gnarl was pretty creepy. The UPN promo guy was right: Ew! Ew! Ew! He definitely reminded me of Gollum though. One slight inconsistently though: Anya implied that Gnarl was one-of-a-kind. So how did demonweb.com know that killing it would cure the paralysis? That said, it was worth it just for the shot of Dawn tumbling off the couch.
Loved Anya. Was her thing about eating the powder her first actual joke? She's said funny things before, but off the top of my head I can't think of another instance of her making that sort of teasing comment before. The closest analogue I can think of right now is saying "That's still funny, sweetie" to Xander's "Respect the cruller and tame the donut!" routine in OMWF.
Lastly, I thought Willow looked amazing. The long hair really suits her. CUTE!