It's the same for every Avatar-God-Gale, I just did a last minute face-heel turn to see the ending and draw my observations from that. What impressed me most about ... no, let me rephrase that: I think that Gale's endings are overall tremendously well written in the sense that they are incredibly reactive and both thoughtful as well as fun (or deeply sad or disturbing in some cases). A point the impressed me a lot was when I had to make the choice on how to continue his and Spawn-Astarion's life together. I thought that Gale would probably love to return home to Tara and his mom, but that this might not be Astarion's first choice. So I chose to help Astarion walk in the sun again. When during the epilogue I opened Elminster's letter, the old sage commented on how unusual this new lifestyle was for Gale. The game had recognised my choice as character development. This is fantastic but only makes sense if you keep the basic personality of your character in mind.
As for the metagaming, from my perspective there are different types of it. There is the metagaming that is a vague plan, like whom you want to romance and which ending you are gunning for. (I am currently playing Shadowheart and wanted to romance Lae'zel. I have no idea which ending we'll end up with, I'll see where it goes.) And there is metagaming which is meticulously planning the outcome of every possible major and a few minor events to achieve a certain ending with a specific interpretation, which is how your version of evil Wyll sounded. I find the latter very unattractive to play because that for me would be like watching a movie or following a script - that is more what I would write fanfiction about.
Crimsom, to my understanding, mostly made an sort of elevator pitch, painting an exciting picture to inspire the imagination in a certain direction.
