Honestly, that doesn’t look too bad. I’d say the plywood is filling in an area of concrete that was removed before. The smooth mortar stuff is self-leveling compound, the gray stuff is concrete. Is there any movement in the floor, and if you’re planning on putting down tile, then movement is the enemy. In which case, I’d say tear the concrete out and rebuild the rest of the floor with plywood, screwed to the joists that are presumably inspected and reinforced if needed.

If you don’t have time or money to do that, this could be used as is with some repair of the holes. Those cracks aren’t really a show stopper, and depending on the flooring you plan to use, you might not need to do anything about them. The concrete debris in the walls annoys the shit out of me, though. And I’d fix whatever you’ve got going on over by the toilet, that looks grim.