recently finished the game and I am currently in the post game.
For me, the fighting is probably the least interesting aspect. I don't care for pokemon and it is like a simplified pokemon. The monsters do auto attack but you can get books to get them to focus on a particular strategy. For example, feed your monster "attack" books and your monster will use physical attacks more than anything else. All monsters have a physical attack, an elemental magic spell (including heals) and a buff/debuff, all monsters can guard and all monsters can sit there and do nothing. Attack, magic and special attack (which are player activated when the gauge is full) can level up with use and become stronger. All monsters have a passive trait that can not be changed. You can equip an item to your monsters and most of them have drawbacks. Monsters have a rank from E to S and can also be rare or legendary. As you level up your watch, you can capture higher tier monsters. You can boost your chance to capture monsters by giving them food they like. Food is in categories and tiers. More expensive food gets better results. There is also sometimes a blue or yellow orb floating on the battlefield. Hitting it with "target" gets you bonus exp, money, items or a boost in recruiting one of the monsters you fought. There is also a monster which makes getting other monsters easier. You can enter codes for in game rewards. You can catch "criminal" monsters (which you don't actually fight) to get a "letter" in a password. You can get coins to put in the magic in game gashapon to get random things, including level 1 monsters. You can scan bar codes of toys you have purchased in real life to get the corresponding monster in the game. (or scan off youtube, like me). New content is still being generated for the game. There are "dungeon" like areas and a town map (divided into downtown, old part of town, etc) with no encounters unless you seek them out by looking for them in trees, under vending machines, etc.
The more interesting part for me is the atmosphere and the humour. Almost all monster names are puns. Example: darudaruma (darui meaning feeling lazy, no energy and daruma being well a daruma). As you may expect, there is a lot of Japanese folklore and culture in the monsters and in the plot. Generally, monsters are cute.
The atmosphere of the game is similar to boku no natsuyasumi or the other level 5 title kaibutsu ga deru kinyoubi. You are a grade 5 boy or girl during summer vacation. You can catch insects, fish, go exploring, talk to friends and do everyday stuff. You can buy a lot of every day items.
Fishing and bug hunting is ok. You spin a roulette, trying to land on a part that is yellow or red. Red gives you a rare version of that insect or fish which you can trade for rare goods at the bug shop.
To find youkai you need to keep your lense on them long enough for them to be fully visible. Higher Rank monsters move a lot and fast while you do this. Some monsters on the main map offer you quests or items without fighting.
The plot is everyday life. Suddenly you go to the youkai world, beat a guy and the game ends. There is a post game so the ending is not really the end. The game has a ton of sidequests. Sidequests also have a chance to give you a bonus reward. A skit plays and if it goes well, you get something. If there is a problem you get nothing. If it is wildly successful you get something nicer. Some sidequests appear to come back (ones where you need to defeat x number of monsters or hand in something). Some purple treasure chests also seem to respawn.
Other functions: look for youkai in real life. Take pictures of people with your "lense". You will youkai in the picture based on the shape of their face? It seems to be able to tell the difference between male and female faces and one person can generate more than 1 youkai.
Game has day and night transition and sometimes it rains. During night time a "boogyman" like event can spawn. As you would expect from a Japanese game, it is full of small details (like taking off your shoes when going in your house).
There is pvp.
Game doesn't really get hard or require much strategy until the end game.
I quite like this game because of the atmosphere and that it feels like being in a Japanese city as a child.