Fun and sweet! I mean, it's Susan!!! And a great-grandchild for the Doctor!!!

The story is nothing groundbreaking, and I'm not sure I like that a) Susan almost causes an alien invasion by naively asking random aliens for help and b) the way the xenophobes end up kind of having a point, as the aliens that answer Susan's call really are there to enslave and oppress them. Nevertheless, it is a much, much, much better reunion for Susan and the Doctor than the EDA 'Legacy of the Daleks', which is also based on the premise that the Doctor gets a distress signal from Susan and goes to 22nd century Earth to investigate.

They mention Susan looks older than the Doctor, so I guess she could somehow control her aging process? I was gonna say Alex is too bratty for my taste, but from his perspective, it really was a lot to take in: famous parents, dead dad, influential politician (?) mum, he gets manipulated by the xenophobic alien haters. Suddenly there's also this weird guy that keeps following him and saying strange things and that he knows his parents, and the guy's an alien! The xenophobes want him to shoot the aliens, but his mum calls the guy GRANDFATHER meaning his mum is an alien as well, making him HALF-ALIEN! And great-granddad has a time machine, and mum wants him to go to space college in their planet... Oof. I'd freak out as well.

Looking forward to seeing Susan and Alex again!