What? It's that quick to complete?
How long gameplay is the first one? I might be able to play through both in an evening.
I know them off by heart, hence why it took so short a time. Gameplay is a hard thing to measure from this type of game. It takes as long as it takes you to beat, you could get stuck and spend hours trying to figure out one puzzle. They can take a while for people that aren't used to the sometimes warped thinking required for some of the puzzles. Stick with it and don't use a guide I say.

If you don't you'll easily get 10+ hours trying to puzzle your way through, if not more.
If it helps, the second game has about 5 times the locations, and it's less linear.
This kind of game would sometimes last me months when it was new when I was a kid.
I agree with some of your stuff, but not all of it.
1: The original viewport is 16:9, and the new hand drawn backgrounds are a perfect match for the original. Change from one to the other and you'll see. They'd either have to chop what they have, or invent new material to get 16:10, I'm glad they did neither.
2. Disagree, I found it easy to use, even straight from the beginning. Far easier than the first SE.
3. Which content (other than the opening) do you think is missing?
4. Agree.
5. All the main cast are the same as they've always been. Considering the 12 year gap for some people it's pretty good of Lucasarts to round them all up. While some of the bit part characters had completely different voices to what imagined from years of playing the text version, I wouldn't say they didn't fit, or where badly done.
6. iMuse is implemented to some extent, but they had a lot of trouble getting it right. From the sound of it, making a seamless transition with live instruments is harder than with midis. To keep the music matched when you change from new to original the same delay is in the original as well. A shame, but I can't say it ruined the game for me.
If you watch one of the making of videos on youtube, the problems they had implementing it, and the solutions they used are explained.
I like it. I'll always go back to my original copy when I want to play the original classic, but if I want to experience the new graphics and voice acting, as well as the commentary I'll go back to this.
It's not a replacement, it's a tribute.