I've seen people complaining about the treatment of Andrew in that last episode, specifically
( spoiler ).
I am reminded of something from Doonesbury, about the character of Zonker Harris. People would write to Garry Trudeau and ask about Zonker's orientation. Trudeau's response would be that, in Zonk's case, it was more a question of disorientation.
In "Buffy", Andrew was clearly immature, quite frankly clueless, and flailing to figure out who and what he was. He attached himself to the Trio, then clung to the Scoobies like a lamprey when it was his only survival option, convinced himself that he was going to die in the last stand against the First Evil...
...only he got to live. And is getting a chance to figure himself out. Becoming someone nobody would expect him to be. Spike got caught off-guard - and was impressed - by Andrew's double-cross earlier in the year.
Polonius said, "This above all, to thine own self be true." But to be true to yourself, you must first understand yourself, to a degree. Discover yourself. Experiment. Try and find out what you might be, to better understand who you are.
I think that was the point of Andrew's parting shot in "The Girl In Question": that while Spike and Angel were still hung over things in the past, other people were moving on, becoming different people.
How to put it? What was the biggest pre-conception about Andrew Wells?
( Another spoiler )My two cents' worth. And that's probably overvaluing it. *g*