Pretty flowers and colour. Composition seems lacking. They are all just there in the middle. Perhaps if you had them at different heights it would look better.
Nice detail, great lighting. Could be a little crowded with the number of tulips included in the comp. Seems a tad oversharpened. All JMO of course. :) Good luck in the challenge.
I like that you didn't use a super shallow DOF on the front flower, some of those are nice in a challenge, but it's great to have the other point of view.
The background looks a touch red on my display and rather spoils the otherwise perfect shot. Might have been worth trying a landscape aspect ratio and using a large apature to get some DOF going on
I'm not a huge "still life" fan but this is a nice shot. You've done a great job of drawing attention to your subject, not only by placement and prominence but in it's subtle difference from the rest of your flowers. Nicely done.