Looks great to me.... except...... I wouldn't use the word cheery (nothing wrong with it just my preference) maybe you could use happy or fun. I say something like ' I like them because they look fun and the place you took them looks amazing'

Dear Tom, Hi! I've just received you photos! Thank you very much for them. Who took these awesome photographs? I like them because they are very cheery and the place where you took them is just amazing. I'm sending you some photos from Paris in return. See you soon! Love, John [You were pretty good. I took out "Something's happened!" not because it is grammatically incorrect, but you just wouldn't hear it put that way. I'm assuming that what happened was that you received the photos.]