It was okay, kind of reminded me of Firestarter in a way, with an adult on the run with a little girl for a shadowy organization. I thought in the end the way the virals came into a person's mind for extended talks was kind of repetitive and boringly staged - it also made them not seem very scary, but rather dull instead. But I'm not sure the series was meant to be scary.
Also the security protocols in Project Noah were loose to say the least. They still put Brad and Amy togeher after retrieving them with great difficulty, Amy and Carter could communicate by simple means of exchanging slips of paper under a door, security codes are pushed in full sight of Brad and Amy so Brad can easily get out at night etc.
And initially, before Amy got special powers, it seemed a lot of fuss about a regular girl. The reasons for not moving on to another orphan girl were rather simply handled, there was no real reason not to do that.
I'm also not sure what the title refers to? The passage to becoming a vampire? Is it the tunnel which Amy is asked to go through by Fanning in one of the last episodes?
On the whole I thought it was kind of okay, but nothing special.