I dislike the default cave tiles. I don't think it is possible to create a decent level with them.
More concerning your level... it is full of tile errors, mainly the water/wall area. Err... it just seems like a bunch of tile errors in the walls as well.
Just for nostalgic reasons I will post of a few of my levels. Maybe you could adapt my style to your own.
Link 1
Link 2 (ignore the south door, it would resemble the door in the first link).
You might find a few of my levels up on Classic aswell, maybe someone could post them or something.