The thing is, “an isometric game” covers a lot of ground. Some isometric games are just regular top-down 2D games that happen to use sprites drawn from an isometric perspective, even though the games use normal rectangular hit-boxes for collision and movement (though I can’t think of a well-known example off the top of my head). Other isometric games (such as the original Diablo and Diablo II) have everything happen on a regular square grid, then they just draw the grid with isometric graphics. That way, game logic and collisions are still pretty straight-forward, but the game looks more interesting with more overlap than a regular 2D top-down view. Still other games use a real hexagonal grid, which makes logic and collisions more complicated in exchange for being mechanically isometric (the same cost to travel in any direction) as well as visually isometric (a thing looks the same size no matter which way it’s pointing).
Which of those seem the closest to what you want?