I recommend with DLC because the DLC adds a lot of items, but the base game is totally just fine.
Isaac is extremely luck-based, so be ready for runs to go really well or really bad on a moment's notice; that's part of the fun is adapting to various items that you get and enemies that you encounter.
I recommend getting some mods from the Workshop that show you what items do, as most of the time the item descriptions aren't helpful at all.

EDIT:
Playing Repentance+ with a fresh save file makes the game feel a lot better than it was before. A bunch of items don't feel totally useless and they all contribute towards something.

[h2]TBoI: Rebirth (with DLC) is a fantastic casual game jampacked with content that'll offer hours upon hours of fun.[/h2] I recommend with DLC because the DLC adds a lot of items, but the base game is totally just fine. Isaac is extremely luck-based, so be ready for runs to go really well or really bad on a moment's notice; that's part of the fun is adapting to various items that you get and enemies that you encounter. I recommend getting some mods from the Workshop that show you what items do, as most of the time the item descriptions aren't helpful at all. EDIT: Playing Repentance+ with a fresh save file makes the game feel a lot better than it was before. A bunch of items don't feel totally useless and they all contribute towards something.