Like most Zelda games, this one has a “gimmick” to set it apart from other games: after the first main level, you can “merge” into walls and travel horizontally, i.e. through narrow gaps or over pits. This is a very important change, especially in such a familiar-feeling world, and there have been many times where I got stuck just because I forgot I could do that. It definitely introduces involves some clever puzzle-solving situations.
There’s also a distinctive change to the game mechanics. A Link to the Past has stood out as the longest game in the series, with 12 levels (although some are quite short). It also preserved a now-rare feature from the original game: you can often enter and even beat levels out of order. A Link Between Worlds appears to have the same number of levels, but it takes the level-reordering feature a step further in that in most cases, there is no order. To facilitate this, the levels often do not contain required items. This is a jarring change and a departure from the series. At first I was a little taken aback when the game just handed me a bunch of items near the start. (You have to “rent” them, but money is pretty plentiful in the game.) After playing it, though, I think it works. Each level does sort of focus on the use of a particular item, so you have a similar feel of solving unique puzzles in each level, and the levels do have important optional items to find. There's also a healthy supply of items to find as you explore the overworld.
Another thing I noticed is that, while the game is clearly supposed to be set in the same world as A Link to the Past, it does reinterpret the ending of that game a bit, since the Master Sword is back (despite the fact that the ending credits said it was to sleep again forever), and Ganon has apparently not been completely destroyed, as the Essence of the Triforce said he had been. But I can’t really complain about that, since those are both key elements of A Link to the Past (and Zelda in general).
My favorite thing about the game is the enemies. Pretty much all the enemies from A Link to the Past are back, and while they’re more detailed, they’re not restyled; they look like they were pulled right off of the Super Nintendo and rendered in 3D. Some of the monsters are absolutely adorable.
I’m not done with the game yet, but I imagine I’ll rank it right near the top of the series.
[Update, with spoiler alerts]
I finished the game! I'm very happy with it. I did manage to skip some should-be-obvious stuff early on, most notably the Pegasus Boots, which I didn't get until just before the last level. Likewise, I didn't know I could purchase (or upgrade) Ravio's items until that point either. At least there was still the Treacherous Tower left to do, and of course the final level, so I did get to use my stuff. I was a little weirded out that they had done nothing to explain the inverted Triforce symbol that's so prevalent, but fortunately they do explain that in the ending sequence, which was very gratifying. The game was definitely easier than most Zelda games; the only game over I saved was in the first level, where I hadn't saved intermediate progress. Later, that wasn't very necessary. I even skipped the red tunic - mainly because I think the blue one looks better, but also I suspected that I could handle the rest of the game without it. (Actually I probably could have done it with the green tunic, since I only used two blue potions in the final battles.
I will say that A Link to the Past is still my favorite Zelda title. And while the graphics in A Link Between Worlds are delightful, I doubt that people who haven't played A Link to the Past will fully appreciate their glory. Same goes for the many parallels between games. But this was definitely a wonderful sequel. Eventually I'll play it on Hero Mode and see how knowing stuff in advance balances out the harder enemies and stuff.