There's a LOT of teeny, tiny details in your design.  Remember, you're printing on a "canvas" that's only 2.5 inches wide and 3.5 inches tall.  Some of that fine detail will be practically invisible to the eye and might not even be printable.  You don't want to be overly complex in your designs - some detail is good, too much detail is not.  Think along the lines of some of the most popular, classic card backs, like the Bicycle Rider Back, the Hoyle Shellback, The Tally Ho Circle and Fan Backs, etc.  Their overall "density" goes only to a certain point, no further.  As a rule of thumb, if you can print your design to actual size and need a magnifying lens to see all the details (or your printer can't accurately reproduce them), that's a sure sign you may have too much detail going on.  There are exceptions, as with any design rule, but if you're going to break a design rule, you really need a good reason for doing so other than "I didn't know any better" or "I just felt like being different."

Back designs are important - but they're hardly the entire picture.  What about the faces and the theme?  What about the tuck box?  It's hard to evaluate the design on just one element.  It's like building a house with a blueprint of just the garage or the basement - it's a nice start but not enough to go on.

Hey there!  First off I commend you on your effort and passion to design a deck of cards.  The creative process is a difficult hurdle to overcome.  Seems like your using a Kung-Fu theme or similar.  I like how the hidden writing is presented in the top and bottom borders of the art.  I do feel that your overall inspiration is lacking solid direction.  It's not enough to pick a theme and hope it sticks, you need genuine inspiration.  It's easy to say that when I'm not the one doing the art but it helps to immerse yourself into the theme on a deep level.  Your attempting too much detail in the bottom and top sections while your fade to a more simple concept as you near the center.  I feel lost when trying to like it.  Your design needs to flow more fluently. I do also like the second color scheme with black and bronze.  There are others here that can critique you in more specific ways but I hope this helps.