There is so much wrong with that.
The pointing is missing on the back. Also, the tiles have been lifted behind the chimney and two of them have been broken. One of them is not seated correctly. The ridge tiles have been loosened and the mortar cracked.
So two tiles need to be replaced and one reseated. I am guessing that there needs to be a new piece of felt under those tiles. The ridge tiles need raking out and re-pointing and of course they need to repoint the chimney. They also seem to have been pretty mean with lead. It's not really enough and there are holes in it.
All in all, they did more damage than they fixed.