From a designers point of view, the concept is still very basic.
However, if you decide to continue on this route it may have some great outcomes.
Here are some tips that can make the back look a lot more interesting.
Colours:
The red and black looks fine, gives it a professional image. The white on the other hand pulls away from the red and black. Maybe something more subtle?
Font:
Your font. its awful. if you want minimal design why use serif fonts (like times new roman)?
Try using clean san-serif fonts. this is very important because serif fonts are just plain ugly if you do not use it correctly.
Size:
The spacing between the words are a bit too much. Try pulling them together closer. you will see a big difference in the design.
Design:
A smart tip, rotate the words to a 45 degrees angle. If you want to create a two way back design which a lot of magicians like, you can try pairing up the words. have to words, in your case "spades" one at 45 degrees angle and the other flipped over. pair them up like that to create a pattern.
Try this and you will see a great different in the outcome. it will be more professional and minimal (no serif font). much cleaner (use either all caps or non caps) -> Spades - NO, spade- YES, SPADE-YES.
hope this helps!