I was able to play about two hours of Mario 3D All Stars so far once 12am hit. And I tried out all 3 games.
I have to say, I'm quite surprised by how beautiful these games look in crisp HD. Going into this I didn't expect the games to look this gorgeous in HD since all Nintendo did was pretty much just upscaled the resolution with very little to no texture work done. However, the artstyles of Sunshine and Galaxy age so well that seeing them in HD legitimately makes them look like modern games and they're beautiful to look at. I'm amazed at how beautiful these games look now. This is probably what Nintendo pictured these games to look like at the time of making them however obviously hardware limitations prevented this, but now in HD they look amazingly good.
I know there's definitely a crowd that's disappointed that these weren't full on remakes or they didn't put much effort at all in improving the textures. However, I feel like games like Sunshine and Galaxy just being upscaled to an HD resolution is really all I need, because those games age well enough in terms of poly count and textures to look beautiful in HD, and I don't think a remake in the Odyssey engine would look THAT much better than what it is now. Plus, I'd rather Nintendo focus their efforts towards making the next 3D Mario game rather than wasting time making remakes from the ground up. I'm completely happy with these games just being rendered in HD, they still look beautiful like this.
Honestly I can't imagine ever going back to play the original versions of these games anymore, the ports on Switch look so much better. I recommend anyone who's on the fence with this collection to pick it up, even if you already have these games the HD resolution makes a world of a difference that you won't want to miss out on.