It would have been better if it were only 8 hours long, LoS had so much boring filler and was so poorly constructed I just wanted it to end. Look at Portal 2. That game took only 6 hours to finish for many people, and it has incredible attention to detail and offers a much more memorable experience. Quality of quantity.
Portal 2 and LoS are COMPLETELY different games. What is good for one game is not necessarily good for another.  That's like me saying that I can play through a game of Pac-Man DX in about 10 minutes, and so since I enjoy Pac-Man DX so much, LoS should follow suit.
Not to mention that LoS is the most beautiful game I've played this gen sans Red Dead Redemption. LoS has "incredible attention to detail" in spades. In the environment, character models, menus, story, ect..., LoS is incredibly detailed.
Honestly, I think this one just comes down to opinion, or maybe just attention span.  There were so many 
wow moments throughout LoS where I was not only impressed, but in truly awe of it's beauty. Saying a game like LoS would've "been better if it were only 8 hours long" means an enormous amount of the game simply wouldn't be there, and thus I would've missed out on some serious enjoyment.
Just out of curiosity, how many games do you play, and how often? I ask because most of the people I know that play a large amount of games (meaning they frequently are playing games new to them), tend to miss out on most of the details I notice when I play some of the same titles, as well as being more likely to get bored easily with a game if it goes beyond the 8 hour mark.  Although, perhaps you're just a busy person, and don't have the time. But then, for me at least, that would mean I would just be able to play the same game longer, which I enjoy. So once again, 
attention span seems to be the culprit.