Lots of Riley haters here...I'm not his biggest fan, but Riley was relatively interesting because he took on the role of the insecure boyfriend. Previously, when the Initiative was pumping him full of drugs, he was rather strong and reliable. Season 5 introduced his weaknesses. With the addition of Dawn, Buffy regarded Riley a just another person she had to look after, someone else she had to protect. I'm glad he finally left, but I think his character was sufficient. Remember that originally Buffy liked him because he was a normal guy and that's just what she wanted. Then she found out about his soldier status and ended up accepting him in spite of it. Ironically, when he became a real normal kind of guy she distanced herself from him. The one thing I like about the Riley story line is that it addresses those inferiority issues that all the Scoobies have with Buffy. As for willingly being bit by vampires, I liken that to Buffy's experiences with Spike in S6. They, Buffy and Riley respectively, both craved something--emotion and desire, to be able to adequately feel-- and had no way of appeasing those sensations and so they sought solace in a deep and dangerous place.