I don't believe they have a director for Halo as yet.
I gotta know how he keeps getting work. I really want to know.
AvP made money. I think the RE films did too.
As for why AvP failed (critically):
Any potential character development with Weyland and the Miller/ Verheiden relationship was quickly snuffed out. Lex was dull as was Exposition Boy.
For more whinging check out the 'What did you think of AvP' thread.