There are some basic collectibles in main game, which will most likely make you replay the levels.
No NewGame+ at the moment, but if you want to go for 100% achievements, then you need to finish the game in 4 hours (so probably on your second save, unless you want to rush your first playthrough).

Once you finish the game, you unlock around 80 different challenges / fights where you can compete against other players (there is a leaderboard now).
Just keep in mind some of the challenges are quite hard and there aren't any guides online at the moment so you really need to figure them out on your own. Also, the leaderboard is quite new, so there aren't that many records / players yet.

B3RKY の投稿を引用：

There are some basic collectibles in main game, which will most likely make you replay the levels.
No NewGame+ at the moment, but if you want to go for 100% achievements, then you need to finish the game in 4 hours (so probably on your second save, unless you want to rush your first playthrough).

Once you finish the game, you unlock around 80 different challenges / fights where you can compete against other players (there is a leaderboard now).
Just keep in mind some of the challenges are quite hard and there aren't any guides online at the moment so you really need to figure them out on your own. Also, the leaderboard is quite new, so there aren't that many records / players yet.

You unlock these challenges halfway.
I made a video guide at least for the first world.

Starting here: https://www.youtube.com/watch?v=6nNUNIhIgYA

@OP
The game has very high replay value, because that's basically the premise of the game to optimize. You will not play the campaign but the individual "Fightments of Battle" these are more difficult versions of all the main levels, every single of of them has several modifier where most of the game will make you approach the levels differently. Sometimes enemy types and positions are remixed

You can earn Rankings for every Figments, additionally thanks to the latest patch you can now also compete in leadersboards as an additional incentive for optimization.

You are right, you unlock them somewhere in the middle of the game. I forgot, my bad ...

But to be fair, unlocking all your abilities and runes first before trying to S-rank everything should be your priority anyway :)