Find a landscape you like.
Take the filter off.
Set the lens to infinity.
Make sure the sun isn't shining into the lens.
Close the diaphragm to f/8.0
Take a light reading off the ground/mid-distance (don't meter sky).
Put the camera on a tripod/fence (if possible)
Shoot several shots, bracketing the exposure (= also using faster & slower shutter speeds than indicated by your meter).
If your shots are then less than vivid & sharp, there's something badly wrong somewhere (the bracketed shots might help track down an exposure or shutter problem).
A new lens is *not* the solution, unless yours is defective or you want a different focal length.