I kinda always knew that Snape didn't "kill" Dumbledore...JKR gave it away a little bit when Dumbledore said "Please" to Snape. Dumbledore is portrayed as such a strong and fearless character throughout the books and him "pleading" to someone who's trying to kill him just didn't make sense or go with his character. I knew there would be more to it. While I was extremely shocked and heartbroken at Dumbledore's death, there's a lot of foreshadowing in the book about his death. The first time i read the book i was crushed, and thinking omg what's Harry going to do now. Not only Harry, but I think the readers looked up to Dumbledore for all the answers, so it definitely felt like "OMG we're all doomed." lol dramatic i know, but yeah it was very devastating.