The Power of Six is the continuation of the storyline begun with I Am Number Four. This novel adds new characters and brings new items, weapons and abilities into play which was just enough to keep the novel interesting. The additions were also just enough to make me care enough about the story and enjoy it. However on the whole I must confirm that while the series appears to have an interesting premise that's a little different (if full of cliché but then I don't think the use of clichés is necessarily bad writing) the writing is average. There is little that separates it from the usual YA novels, nothing that makes it a Revenge of the Witch, The Knife of Never Letting Go or The Hunger Games. You may want to stop reading here if you intend to read the first novel at all. If not then please by all means continue.
The story follows two different protagonists from their first person perspectives - Four or John Smith - and Seven. In Four/John's world he is on the run from law enforcement with Six and Sam and still trying to come to grips with his new alien powers. In Seven's world she is trying to work out how to live her life as a super-powered alien in a Spanish orphanage that really seemed a lot more like a convent. Seriously what is it with Spanish Convents orphanages and novels?
Anyway in conclusion this is a book you can give or take about. It's certainly no masterpiece but neither is it brain-fryingly-awful. It's the deep fried version of a book, containing lots of fat and probably not going to help you develop any literary skills but certainly fun enough to read at the time. But also utterly forgettable. I certainly won't remember this story until I read the next novel because it's merely momentary reading fun.