Um... Haven't you read last news? Computer scientists at the University of California discovered a totally new, 24-th pattern! Sorry, but GoF book is obsolete by now!
Kidding.
I read both books and I would prefer "Design Patterns Explained" to start with - because they marvelously explain what patterns are, what underlying theory, or call it
philosophy, is, and how to "think in patterns".
"didn't discuss all core 23 patterens" - unfortunately there is no way to memorize "all core 23 patterens" and be able to apply them. You need to understand what you are doing!
What is better: to memorize first 23 prime numbers or to know what prime numbers are and what the formula is, and to be able to calculate next 123 or how many you need yourself?
After you read "Design Patterns Explained" - you can read any other book on patterns, with "core 23" or whatever