Depth of field is too narrow. I'm assuming you were close to the subject and shooting with a low f/number. Try using a larger f/number to get more of the subject in focus. Compositionally, there is nothing interesting going on -- most of the flowers are centered, which contributes to the dullness. Try placing things off-center, and use the foreground/background together to create depth.
Thank you Reznap. I grew up in a country where there are no dandelions. So they are fascinating to me. I appreciate your CC. Very helpful. Have a good one!