The game was really good when I started it. The first 20-30 adventurer ranks went in a breeze. Now, in adventurer rank 40, the game is getting quite repetitive.
The quests I have left are story guests, which don't seem to be too interesting, as they're usually just errand running simulators.
Daily quests, which we get 4 a day are done quite quickly. Not enough to keep one occupied for more than 30-45 min. Other than that, you can explore the world or just level up your characters
The game is enjoyable for a free game, the exploration is great as long as it doesn't get repetitive (damn you 3 surprise slimes! Frick off!).
In conclusion, the game is definitely worth a download, but just don't put any money into it. Or you can. I'm a sign, not a cop. The game is good fun for around a hundred hours, and the fact that you're eventually going to get bored of it shouldn't outweigh the amount of entertainment you could have. Just remember, be careful with the gacha. It's literally gambling, and a lot of people get addicted to it, and addiction always starts from the "huh... This is neat" feeling.