morphing jar is an ok card, but there are better cards to play with. yes morphing jar first turn with an all monster hand is broken. but morphing jar is way to slow for your main strategy.
all you do is keep doing draw cyclus with gates and plus out of it. morphing jar requires 2 turns, 1 of you, to set it and your opponents turn after that. there are so many ways to get rid of morphing jar and if you depend on it, you are pretty much screwed.
and isnt it obvious that if you set a field spell (or activate gates) and then set backrow and a set monster, that its a morphing jar? ppl will play around it or get rid of it. either way morphing jar is an ok card, but there are better cards to play with.