I would stain it darker.

I would paint it. You have to check with the paint store as you don't want dark spots coming through the paint. Best wishes.

Agree with laurie. Prime with stainblocking primer, and paint over it. The dark spots are competing with the fireplace.

Pick a tan or grey shade from the fireplace stone. Paint the paneling and the ceiling the same color.

Brown walls, brown furniture, brown chair: too much brown, so I'd paint the walls.

I would retain the paneling ( if it is tongue & groove) on the end wall with the clock on it - in a few years it will be very popular again, though two walls are too much, I agree. I would completely remove the paneling on the other wall and around the FP thus making the end wall a feature wall. I think the one wall where the paneling goes up to the peak of the ceiling is quite attractive and very appropriate to a casual decor. If the paneling is tongue & groove and you paint it, it will always show the grooves, which isn't so great.
Tearing out the paneling and replacing with sheet rock and paint will change the whole character of the room.