I can't speak for Shadow Wars, but avoid Rayman Origins on 3DS unless that's the only way you have to play the game. It might be a great game, but the 3DS version is a bad port that has some nasty framerate problems and graphics that resemble a blurry washed out lowres youtube video. All other versions on other systems are superior by far. And the game was released on 360, PS3, PC, Vita and even the original Wii.
Even if you don't have a console or Vita, you might have a PC capable of running the game. I've a lot of experience with the PC version, and it's actually incredibly light on system requirements compared to pretty much all other PC games of its time. I was even able to run it fullspeed @720p on a non-gaming PC with a weak processor and even weaker graphics card (Athlon II x2 along with a discrete low wattage Radeon 4350 that choked on other PC games even at 480p resolutions). Even if you don't game on PC, you might still have one that is capable of running the game respectably. You can get the PC version for about $20 digitally, the extra $5 is IMHO money well spent for a far better looking and performing version of the game provided you have a PC that can run it.
There used to be a demo on the eshop, might still be there. There's also a demo for the PC version. You should at least try them both out before making a decision. Especially to see if you've got a computer that can run it decently, and to see whether the flaws in the 3DS version are worth $5 extra in your pocket.
I've heard mixed opinions about Shadow Wars (i've actually heard some people enjoyed it), though it at least doesn't have a prior existing version of the game to compare it to. Ubisoft is almost always horrible at porting their pre existing games to Nintendo handhelds and Origins is really no exception to that rule (they couldn't even properly port the Dreamcast version of Rayman 2 to the 3DS). I will say though that if the 3DS is your only hope at experiencing Origins, then go ahead and get it. Still a great game underneath the technical problems, and at least the gameplay wasn't completely ruined like their port of Rayman 2 on the original DS.