Things I liked:

• Sarah Jane <3
• K9 <3
• The scene between the Doctor and Sarah Jane at the end, Sarah Jane finally getting closure
• Sarah Jane's connection with K9
• Rose for the first time realising just how old the Doctor is and what that means for her - it's interesting to see her grapple with that
• On the whole, there were some really nice character moments in this episode

Things I didn't like:

• The pacing felt off
• The Krillitane were under-utilised
• Rose and Sarah Jane's fighting. I like the idea of tension between the current companion and a previous companion, but I don't think it was done very well
• I felt Mickey was the only one of the main four in this episode that lacked any particularly meaningful character moments. It makes sense for the focus to be on Sarah Jane, but considering this is the episode Mickey joins the TARDIS team, I do think he should have had more attention than he did

Overall, while this episode had a few really good moments, as a whole it doesn't work that well for me. It feels like it's trying to tell two separate stories - the emotional journeys of the characters and the main plot with the Krillitane - but the former comes at the cost of the latter. I think with creatures which change, adopting features of other species, there was an opportunity to link that to the theme of making the most of the present and learning to move on from the past present in the character's. Instead, the episode largely keeps the Krillitane plot separate from the character work, which I don't think works in it's favour.