@Lelygax I meant exactly what I wrote. Side quests and exploration(secrets) were included - for example, there were very few heart pieces I didn't acquire. If I rushed through everything I did and never paused the game, it would've been 65-70 hours, no side quests.
I don't see how you can artificially lengthen a game which you don't level up in unless you're leaving it paused to let the counter keep ticking. I personally find games always take noticeably longer on the first playthrough, but this is still considered a lengthy game.
I would recommend watching some TP reviews, I'm not the only person who believes there's enough content for more than 1 game here.
I was sleepy at the time and thought you said Skyward Sword (yeah, THAT sleepy). I've played Twilight Princess on Wii and finished it without getting all hearts too, because it was getting boring too.
Maybe its the "feel" or "aura" of this game where they tried to make it feel like a desolate world, but I really felt a lot of areas boring or as if missing things (even if they don't, it was on purpose). This feels even worse than artificial lengthening to me because its made on purpose, so its big for the sake of being big, feels empty and they know it feel empty (not all areas, but a lot of them). When I saw Breath of Wild being a complete open-world game it even worried me it would suffer from the same things, but since I didn't played it I don't know, hopefully not.
To answer it for you, to aritificially lenghten a game it doesn't need RPG elements nor be exploration based. If you get Super Mario Bros 1, double the size of the first level and doesn't adjust the enemy number and placement to it feel good (aka, its not planned from the beggining and you only wanted a bigger level) IMO you artificially expanded the game. The player will take more time to beat this level, it will feel wrong and yet not funny as if it had the original size. Now if lets say, you get a level that was thought to have the double size since the start, or if you adapt the level correctly, it won't feel artificial, there will be things to keep you interested until the end.
Only to be clear I also think that TP is really big, maybe even as big as two games, not only because of the alternate versions of most areas. But the problem is that it doesnt felt as if it had content for 2 games, but had the size, so it became a chore to me sometimes when I needed to backtrack and nothing interesting was happening.
Your post made me re-think some things and remember another, so I thank you for that. The different opinions in this thread are very interesting and enlightening.