First, Isaiah sees God and the angels and such, and is appropriately overwhelmed. He doesn't feel worthy to be there, yet he ends up being God's messenger: 'Here I am, send me.' Then Paul talks about how he's the lowliest of the Apostles, and feels some remorse for persecuting the church prior to his conversion. But then he says 'but by God's grace that is what I am.' And finally, when Peter realized just who was in the boat with him, he said 'Leave me Lord, I am a sinful man' – and Jesus replied 'Don't be afraid, from now on it is men you will catch.' Three reluctant messengers of God, all realizing their imperfections. And it seems to me that with all three God said something like 'Don't worry about that, I can work with your imperfections; you are going to do fine.'
Now if I remember correctly, none of these three guys had an easy time proclaiming God's message. They all ran into trouble – mobs, angry political and/or religious leaders, long and hard journeys and so on – a lot of resistance to change and displeasure at hearing the truth of messages that upset the status quo. When they weren't getting thrown out of towns they were often jailed. Some people did catch on to their messages though, and today we view them as successful prophets.
So back to the 'wow' factor... God is calling me, and each of us, to be messengers. I've been reluctant because I'm not perfect, and I don't want to deal with the resistance to the message. But I can see in these scripture readings that God has done this before, and imperfect people have done this before. It's a proven model, just waiting for the reluctant messenger to do his part.