Let me start off by saying two things: one, I am a HUGE fan of Link to the Past, to the point of absurdity (it was one of my first video games), so I came into this not expecting it to surpass the original. Two, I enjoyed it my first time around, but not as much as other 2D Zeldas, such as the Oracle duology or The Minish Cap. Overall, I found it to be a disappointment, even if I had fun with the game.
This time I played on Hero Mode, and it makes all the difference. Normal mode is simply too easy. Hero mode requires you to stay on your toes. You die. You become more engaged with the game. It's harder than LttP, but still closer to it in difficulty than Normal Mode. Hero Mode makes the game fun.
The map is completely derivative of LttP, at least the map of Hyrule, but that's also where its charm lies. It's fun to go back and visit the old locations again, and see new faces and subtle changes to certain areas. The desert being walled off and only visited later as part of Lorule's dungeons was a nice change of pace and a creative way to design a new dungeon in an old area. I also like how they didn't reuse the dungeons from LttP; even the ones you visit again, like the Tower of Hera, are totally different in their design.
Lorule is a hauntingly beautiful world and, in my personal opinion, much more enjoyable than the series' other parallel universe of Termina. I love its use of purples and blues, and it's visually distinct enough that it doesn't feel like a retread of LttP's Dark World at all. My only complaints with Lorule are that A) The name is a really stupid pun and B) Despite what I just said, it's also true that it's too similar to the Dark World to believe that it's a totally different place. Regardless, it was a very enjoyable experience and the second set of dungeons were very creative.
The portrait mechanic is something I initially didn't like, as I felt it was too much of a departure from LttP's mechanics, but this time around I really warmed up to it. Zelda is at its best when it takes a gimmick and runs with it, whether it be time travel, transformative masks, changing the seasons, ocean traversal, or whatever - and this game not only take Link to the Past's alternate world travelling gimmick, but also adds one of its own with the portrait wall crawling. It added its own unique flair to solving puzzles and felt like a fresh experience.
The rental system, on the other hand, was a nice idea in concept. I don't dislike it. The non-linearity it offers is as refreshing as the new portrait mechanic. However, it also took away the charm of finding a new weapon in a dungeon, and renting items over and over again when you die could get tedious. Despite the tedium of re-renting items upon your death, Hero Mode made the concept more fun, as in Normal Mode you are never in any real danger of losing your items and there is much more of an incentive to save up rupees to buy them.
I also very much liked the upgrades and how they were performed - finding lost Maiamais was one of my favorite things to do. It took the collectathon concept and made it feel substantial by giving you a useful reward for every ten Maiamais that you find. The Maiamais were also adorable.
The story was more absent than it has been in recent Zeldas, but more present than it was it was the classic games, which was a nice compromise between new and old. Hyrule's cast of characters was relatively bland, but where the game really shone brightest was in the inhabitants of Lorule and the story behind their kingdom and its Triforce. Hilda and her last minute betrayal were well done - I never saw it coming the first time around, and she was effective as an empathetic villain.
The ending makes her entire scheme seem intellectually bankrupt, however, as Link and Zelda use Hyrule's Triforce to wish Lorule's back into existence. Why didn't Hilda do this from the beginning? Ravio and his existence as the "other Link" is probably my favorite plot twist in any Zelda game, if only for the fact that we technically get to see an incarnation of Link speak. Yuga was... ok, I guess. Ganon, Demise, Ghirahim, Zant and Vaati were all more interesting villains than he was. Yuga came off as kind of a clown.
Lorule's "Triforce trio" was ultimately a refreshing new take on the three characters we've grown attached to over the course of several games, and their subdued personalities were a thematically appropriate inverse for a world that had its own Triforce shattered. Ravio lacked courage, Hilda lacked wisdom, and Yuga lacked power.
Overall, it was a fantastic game, and a nice return to the "Fallen Hero" timeline of the original games. Perhaps Nintendo will visit it again in the future? One can hope.