Honestly, I moved a lot as a kid, but there were three Sunday School teachers who really left an impact on me. And to be truthful, I don't remember even one lesson they ever taught! All I remember is that:
Sis. Elizabeth, my teacher when I was 6-7, used to be able to tell all kinds of awesome Bible stories. She put a love in my heart of the Bible where from that age (literally 2nd grade) I would flip open a KJV and read it A LOT. I loved it. She placed a love of God and His Word in my heart by showing me all the cool stuff in the Bible. She taught me that it's actually fun to be a Christian.
Then there was Sis. Susan (when I was 8-9), and every single week she would dismiss class as the altar call was starting in adult church and she would take all of us up to the altar to pray. EVERY SUNDAY. At first I didn't know what to pray but she kept on praying with us and eventually I started praying like I never knew possible. Whatever she did, I have no idea to this day, but she gave me a habit that has stuck with me since those days--that no matter what I can always pray and God always listens.
Then there was Bro. Jason (10)--I don't remember anything from his class either other than once he gave us a sheet with Bible verses on it that we had to memorize. And after we memorized them all he bought us each our own Bible. I still have my Bible to this day and I teach Sunday School from it now. I remember my friend and I used to remember it really quick then tell him, just so we could get the mark for the Bible. Well, one day he said, "It's great you want to get your Bible, but do you think it's really helping you any if you don't remember the verses long term and just for now?" I thought about it, and he showed me that Bible memorization is absolutely necessary for the Christian. Now I have my SS kids memorize verses all the time, too
That said, I always make sure there is something in class that makes the kids laugh. We sing this song with motions called, "Jesus You're My Superhero" by Hillsong. There's a part where you shout out "Jesus is better than [insert superhero]!" The kids love just shouting out names! We play games, use puppets, do songs, etc.
One thing that keeps it good for them is that if there's something they want to talk about any given Sunday, so long as its church or Bible related, I have no problem saving my lesson for the next week and talkng about what they want. I taught on Hannah once and all they wanted to know about was what Samuel did when he grew up. So my lesson switched from Hannah to Samuel.
There have been times when kids have come in hurting from family problems, and the kids will ask if we can pray with the kid instead of our normal lesson. Not a problem! If they're doing something for God, isn't that our entire objective? So what if we don't finish the craft or story--if the kids get even one step closer to Jesus the goal is accomplished.
But most of all, and I learned this the hard way, we can have the flashy games and logos and the best music, but if we aren't praying with the kids and teaching them God's complete Word, then we're failing. Because as I learned growing up, I don't remember one craft or song or lesson, but I remember the spiritual blessings my teacher gave me.