A great edit. The core story of season 1 was told in an exciting and fast-paced way. Some story elements do get cast aside and the extent to which they work varies. For example, by losing most of Arya's story with Syrio it actually becomes a fun twist when her "dancing lessons" turn out to be swordplay instead. Losing the entire journey from Winterfell to King's Landing isn't missed at all. In fact, I'm sure other plot threads were dropped with no major effect on the overall storyline (although it will be interesting to see how Bron's inclusion in future edits will play out given that Tyrion's side plot to the Erie is gone). The only real complaint is that Dany's story feels very abrupt - she goes from being treated as property being bartered to being a well respected part of the Dothraki very quickly (in fact, there are two scenes immediately after each other that effectively show the same thing - they like her, but have no respect of Viserys. It seems like only one of them would have been needed. But truthfully, this is some minor nitpicking - when everything else is spot-on, the minor issues just stand out.
The editing is done well. The inclusion of LOTR music works very well, especially the choice to give each family music related to a specific element of Middle Earth.
I've always been more of a fan of the ASOIAF novels than the show which I stopped watching around early season 2. Was quite interested to see this project cutting the seasons down into films, and I'm also a LOTR buff so I was interested to see how the music played.
Overall it's a strong cut well-executed. The music worked better than I expected, but I felt that some of the original music warranted inclusion rather than a wholesale replacement, and sometimes there was just too much strong music constantly without enough time to breathe.
There were some unfortunate digital glitches that others have mentioned, hopefully those will be cleaned up for a better viewing experience but hardly a deal breaker. Also noticeably lower audio quality at a few points.
I thought the narrative worked quite well! If anything I think it could have done with another 20-30 minutes, particularly to develop the Stark children a bit more and make the King's Landing conspiracy slightly less rushed. Strong decisions on what to include and what to cut overall.