遊戯王 (Yu-Gi-Oh!) was released the same year as the first Pókemon merchandise; it is not copy or new take on it. There's a lot to know about the original and 4Kids version of the show in order to understand it and make a decision for yourself or anyone else. I'll start here.
There were many more violent and adult aspects in the original Japanese show that were censored out, including weapons such as guns and daggers, as well as death, murder, abuse, and in one instance a suicidal gesture. 4Kids changed it so there is no death and very minimal violence. Other changes include the persistent and blatant removal of punching, slapping, and hitting of any kind which does, in severe cases, take away from the continuity of the plot. But as far as violence goes, the worst you're going to get here are some aftermath band-aids. When it comes to sex it's the same story as with the violence. The original manga and anime contained more – some suggestive or revealing clothes on women, and brief implied nudity (male) in a few cases. Also, in the original show Yami (Atem) calls Yugi “aibou”, which literally means “partner” but often, and partly as a result of the Yu-Gi-Oh! original and abridged series, takes on a homosexual connotation. This, however, is also omitted for the English dub. But all in all sex is not something to worry about in either show. Consumerism – What people need to understand is that both the manga and the anime were released before the card game. Today, it's much easier to interpret the show as a commercial for the game but it simply isn't true.
You can rest assured this show is intended for a young audience and though there is some “scariness”, it's safe for just about any age. The only reason I recommend a higher age is because the show does retain a moderate amount of depth, complexity, and moral examination. The majority of this comes in the fourth season when some characters, including one of the protagonists (Yami/Atem), become evil due to the “Stone of Orichalcos”. Much of this season is spent with him doubting himself and trying to figure out who he is/was and what he believes. Most of the other seasons are more shallow, but with strong continuing positive messages of friendship, loyalty, honesty, courage, and kindness. One of the great features about this show is that the older you are, the more there is to understand and like about it, so it's not limited to kids.
All in all I would recommend this show to just about anyone. For older viewers (At least 13) I would also suggest the manga or original Japanese version or possibly Yu-Gi-Oh! The Abridged Series, a very hilarious take on the show (Again, older!).