Despite not being clear on the box, Rayman 3D is a port of Rayman 2: The Great Escape. In this game, Rayman starts out weak and powerless, captured by the robot pirate Admiral Razorbeard. His cell-mate, Globox hands Rayman a silver lum (fairy-like creatures) which was given to him by Ly the fairy. This restores his powers enough to make his escape from the pirate prison ship. Rayman then sets out to find Ly to further regain his powers. From there he is given the quest to save the Glade of Dreams, and to do so, he has to recover the four masks to give power back to the spirit Polokus to assist in stopping the pirates.
Scattered around the levels are a total of 1,000 yellow lums and 100 captives. A few of the levels require a certain level of lums to progress, but the requirement isn't too strict as it never halted me despite never straying too far to collect them. Each level offers the chance of playing a bonus stage if you do collect every lum and captive within. The collectables mean that completionists will replay levels to collect everything, although I don't think there's much motivation to do so.
There are also a few other variations of lums which are useful within each level. Red lums restore Rayman's health, green lums act as checkpoints, and purple lums are floating rings which allows Rayman to swing from them to cover large gaps.
As you progress, the level design aims to keep things fresh. There's plenty of platforming and swinging over ledges, use of 'vehicles', hitting switches and bringing objects to marked areas. So you will be picking up powder kegs and throwing them at destructible panels, riding a rocket creature over perilous terrain, flying on a rocket keg, riding plums down rivers, and chased by a flying pirate ship over falling bridges.
The automatic camera is helpful for showing you the way forward, but it can be awkward if you want to backtrack to find the secrets that lay outside the main path.
Rayman can walk and run with the analogue stick, jump by pressing the B button, and pressing it a second time causes him to glide. Y is to attack which strangely, he shoots energy balls rather than throwing his fist.
There's not much combat within the game, but it seems a bit over simplified so that it seems like an unnecessary distraction. Once you hit the enemy, you need to wait for him to flash several times before you can attack again. It's a case of rinse and repeat, and Rayman has far more health than the enemies, so it's just a matter of time until they are defeated.
The colour palette is surprisingly dark and there's not as much variation in theme compared to the original Rayman which had a more interesting, vibrant world. This one looks rather dull in comparison.
One seemingly minor thing that was a great annoyance was the fact that every time you load up the game, Rayman is positioned at the start of the island, so you have to navigate over the entire map just to find the level you are on.
I've read a lot of comments about the game suffering from poor frame-rate or double vision on some areas, but I had no problems what-so-ever.
Given that the game is old and has had several ports to various consoles, there's a good chance you will have already played it, or could acquire it for a budget price. If you do want to play it on the 3DS, then it is a decent game, albeit nothing special.