The last and third TMNT game for the GameBoy was a bit different from its precursors. Instead of a simple fight’n run with levels it offered one continuous world. It’s like a prototypical metrovania, with the difference that you don’t unlock new abilities but characters with different abilities. You start with one turtle and your mission is to find the other three, master Splinter and April O’Neil. I say prototypical, because at that time there was no metrovania genre (apart from the first two Metroids and some others who have been retroactively fitted into the genre). So no standard concept of what makes or brakes typical games of that kind.
TMNT 3 biggest problem is that it caters to a skillset more fit for conventional platformers. Endlessly respawning enemies once you leave a screen, levels that punish you for trying to jump from ledges. Traversing the whole map becomes very frustrating and only extremely careful players will get to the end. But since the map is much bigger than conventional platformers, being overly cautious becomes pretty tedious fast. If you cheat (unlimited health), you can play the game more like a modern metrovania and the whole exploration aspect is fun again. But that takes a bit away from the challenge. On the other hand, playing it as it is, isn’t much fun.