Fighting is the main method used to solve problems.
The "N" in the title stands for ninja, and there's a lot of swordplay and animated violence, including an intense battle between warriors resurrected from stone, a group of swords for hire, and the four turtles. Raphael challenges Leonardo to a fight, and they go sword to sword. An early scene set in South America features gunfire.
April and Casey live together and kiss. Mr. Winters flirts with April.
Mild teasing: "knuckleheads," "stupid," etc.
The turtles have spawned an industry filled with toys, games, comcis, T-shirts, TV shows, etc.