As we know the whole idea of the regeneration (it wasn't even named like this yet) was absolutely new and this story was a big risk, hence the Daleks. It not only introduces the new Doctor, but also shows us (for the first time) two types of viewers: the ones who believe and accept the new Doctor (Polly) and the ones who don't (Ben). It's so obvious nowadays but i think it was absolutely brilliant back then and really worked very well. We are beginning to know the new Doctor through his companions and we worry, doubt and wonder with them.

The Doctor faces his greatest enemies but we as viewers also face the new fear: what happened to our beloved character and what's next.

The plot itself it's simple enough to be interesting but not to interfere with the regeneration and it's done absolutely beautiful.

At the same time the Power of the Daleks sets up the new era of Doctor Who: hostile alien planet (Ben and Polly's first actually) and the famous Troughton's "base under siege" type of stories.

10/10 for me personally, but i'm a little bit biased here.