Say what you will about idle games, but I've spent an awful lot of time messing around with them in my free time over the years, and Madtale might be the highest production values I've ever seen for one of these. This gacha-based idle RPG is centered around the fairy tale concept, with the various heroes you can gather inspired by classic children's stories like Snow White and The Little Mermaid.
That concept could be rather bland, but the game handles it well, particularly thanks to its very high quality and detailed character art. It's not just that, though. Madtale also features a surprisingly fun story to keep players wanting to move through levels, and the dialogue even has full voice acting that's certainly better than I'd ever have expected from a free-to-play idle game.
Of course how much you care about any of those details is still going to depend on whether or not auto-battling idle games are something you enjoy spending time on. For my part, I like having a chill, shut-my-brain-down kind of game to play on the side of whatever I'm playing more seriously at the time, and Madtale fits that well. It's the perfect game to pull out and play for ten or fifteen minutes before bed or when you just need to chill.
Do be warned about the gacha, though. SR characters are hard to come by, and you'll need to collect a lot of copies of a character if you want to boost them to their highest levels. There should be plenty to keep you busy before that's ever a concern, but this game could end up leaving you feeling frustrated in the endgame.