izigame.me

Honestly better than I thought. I bought it not expecting much but they added a decent amount of content for the animals. Apart from being able to catch almost every mob in the game, you can dress them up with unique accessories (hats, glasses, etc) for every single one and also change their "skin" to a different colour so yours looks different from the regular mobs. You can also interact with them. That's quite a lot of new textures, models and animation they had to make.
Every time you catch one it adds a proper entry about that animal (like a p*kedex) and when you level them up to a certain level, they learn a new combat skill. You can catch both regular and alpha variants and they are two different entries.
I've only seen/caught 1 shiny so far, they have a sparkle effect and make a sparkling noise when you're near them. The shiny thing doesn't make them look unique - you can change their skin from the menu, so you don't really have to "shiny hunt" like in P*kemon. Supposedly there's a buff but I couldn't really tell because I immediately fed mine and made it rare and high level.
You can catch them as early as day 1 so it does wreck the game difficulty a bit because you can dispatch them out to gather materials and water (10 simul dispatch limit still applies). Usually in regular gameplay it takes a while to befriend the street animals before you can do this. I'm already at end game by the time I bought this so it's just an extra little fun thing for me to play with.
I've also seen a few negative reviews because people have no idea how to get more of the currency or the catching balls. You can buy everything from the Town Hall shop (the one near to the door, not the one where you get your wedding dress) including a new Pet Apartment that houses 5. The pet apartment is massive though. Wish they made it small because I can't fit that many apartments in my workshop.