They look nice and sharp - not sure of the point... are you asking why only these came out good? If you want to know why the "bad" ones didn't come out right, I think you'd be better off posting those. The "grainy" you mention is, naturally, not the fault of the camera or lens.
If you just want feedback on the shots, as I said, they look okay to me. Good luck with that camera.
"There is no special way a photograph should look."
- Garry Winogrand