The Triceratons are attempting to abduct one of the Turtles' friends, and it is up to the lean-green-fighting-team to make sure they don't succeed. That's the basic setup of
Teenage Mutant Ninja Turtles 3: Mutant Nightmare. The game is divided into four worlds, and each world has a series of stages. Each stage should take about less than ten minutes or so to either beat or fail. This is why the game is great for a portable. You can quickly go in, try to beat whatever stage you are stuck on and jump out again in no time.
Of course, this also means the game's Story Mode is a quick play. Though you will have to repeat most of the stages several times before actually getting past it, the Story Mode will probably only take you about seven or eight hours. Of course, you can go back at any time and replay beaten stages if you wish. This, plus the game's other modes (including a few multiplayer components) helps to add to Mutant Nightmare's gameplay time.
These other modes include Battle Mode where you will be confined to a small arena and you must collect a certain number of crystals before the clock runs out. These arenas will have you doing everything from bouncing off of enemies, to jumping on disappearing platforms, to swinging around on poles to get to hard-to-reach crystals that appear all over the room. Though this might not sound like too much of a challenge, the time limit is typically just short enough that it will take you a few tries before you get skilled enough to get to all the crystals before the clock runs out.
The other mode offered is Practice Mode. Here you will select a turtle and learn from Master Splinter how to use that character's various special abilities. For instance, this is where you learn how to call on your allies or use Leonardo's powerful slash attack or Raph's strength.
In fact, that's another difference that I found in this game that made me find it more enjoyable than the GC version. The DS' TMNT 3 actually made the different turtles feel like unique characters. In the GameCube edition, with the exception of a couple of moves, each turtle felt like the next. That doesn't seem to be the case here. I found that Leo was quicker, while Don was slower but seemed to have more of a reach. Raphael seemed to be able to take enemies out faster while Mikey seemed to be a good average of the three.
This, plus the fact that in some stages, each turtle had to take different paths (because only Raph can move the boulders or only Don can open a computer-controlled doorway) helped to make the game feel a bit bigger than it was and make each of the four heroes unique.
The game's Multiplayer component requires that all people joining in have a copy of TMNT 3: Mutant Nightmare. If that is the case, then up to four people can either team up or go head-to-head in the Battle Mode challenges to see who can collect the most crystals.