yeah i finished it too an itw as aweosme but i think snape is still with dumbeldore and infact dumbeldore must have requested him to kill him if any situatioon that arises like this also its very important for snape to be amongst the dark lords good books as he is very crucial to their mission
it was clear when harry eard dumbeldore say "severus please" which infact harry thought was pleading.....now will dumbeldore ever plead with anyone to save his life ......knowing him..i dont think so
also snape prevented a death eater from killing harry indirectly by telling his that voldermort wants to kill him with his own hands
anyway lets see ....coz they have not shown clearly on whose side snape is on ....so lets wait for the next book