I find the vignette fine in the first image, but way over done to the other images.
Take the image with the girl hiding behind the bouquet. Its a cute image, but the vignette is too harsh. I agree that it helps to draw attention to the subject, but I find that you could of shot this image better and drawn the viewers eye more to the subject.
I dont like how she is centered on the frame, the vignette seems to be the band aid to remove the extra clutter that is around her in the frame. Maybe looking for a different shooting angle and being mindful of the background when taking the image. Backgrounds are harder to manage when you are doing candids, but this seems posed enough that you could of moved her.
Moving her into a better light would also help get some light on her face...that or angling her chin up slightly so her left eye (camera right) isn't so dark.
You could of also zoomed in on the person and fill the frame up with her face and the flowers more... longer focal lenght = shallower DOF = blurrier background.
all of the above applies to the second image. No real reason to get all that head space on top of the subject, and yet cutting his feet. I could see a higher shooting angle (so you are looking down on him) and much much closer in to his face...and then another one where you are further out, dont cut his feet, and his head is not smack in the middle of the frame.
I've seen a trend here in the last few months where people think that throwing on some post processing is a cure for images. While it can help images, as I find it helped in your first, you should aim at getting images well composed, angled and exposed in camera.