I quite liked this, though I hasten to add that I studied drama in university and have written plays so I may be more comfortable than some in reading a script. As such, I found it very readable (I presume they've removed some of the more cumbersome stage directions to make it easier to read) and a fun glimpse into the future of the HP characters. As my friend Jo Ann noted, this is more of a postcard than a letter, particularly in script form it's like an amuse bouche. A full novel version of this would be interesting, but for whatever reason Rowling thought it works best as a play. And plays work best in theatres, so I presume you'd get a more full experience watching it in person.