Donkey Kong Country Returns is my favourite game of all time.

This is a tough one, there are some favorites that I've yet to experience like DKCR, NSMB and Warioland Shake It, but of the ones I've played, Kirby's Epic Yarn, Return to Dreamland, A Boy and His Blob and Klonoa (I don't count Rayman Origins, especially since I have it for the 360) I would probably say Kirby's Return to Dreamland has been my favorite so far but Epic Yarn is a close 2nd. Although I found A Boy and His Blob absolutely amazing (the visuals, music, simplicity in execution) I did find it REALLY frustrating at times whereas both Kirby games just took me on a non stop super fun experience. I did enjoy Return to Dreamland more because I actually had never had the pleasure of really playing a traditional Kirby game before and this one did it for me and so much more. I do still intend on getting DKCR when the price drops (Nintendo Selects?)

To me, what makes Kirby dreamland so much better than Epic Yarn are the challange stages, theryre really good fun to beat and improve scores

Probably Donkey Kong Country Returns and Rayman Origins.

Definitly not Rayman Origins, which i just completed btw. I collected all 10 of the skull teath, and finished all of the stages/worlds including The Land of the Living Dead. Although... i do still need to collect 44 electoons, but I'm not bothering because this is hands down thee' most boring 2D platformer i've experienced on the Wii...I basically forced myself to finish it, just to see the very end....Including 2 screens of overly long credits.lol

Yes, the visuals are absolutely gorgeous. The environments are outstanding(Jiggle jungle being my favorite) and the amount of depth and variety is wonderful. It's an amazing feat and ubi should be commended...I haven't seen anything like it in a 2D Sidescroller. Yet I was divided on most of the music...
Some of it was pretty great and perfectly captured the wonderful atmoshphere, But the artsy fartys chipmunk pieces started to get annoying after awhile, especially the LUM JINGLE which happens everytime you get a sleeping LUM. As for the gameplay, it just feels extremely uninspired....And very repetitive. It has a 'hint' of feeling/controlling like a flash game, and I was dissapointed at the lack of challenge....Aside from the treasure chasing, the 6th world(Cloud area) is when the game starts to pose any sort of challenge, while the Land of Living Dead totaly kicks it up a notch, but sadly is over before you know it. I don't feel like it lives up to the hype...It does with the visuals, but it falls a bit short in the fun factor department. I know i'm definitly in the minority on this one, but eh.

So far in order from Favorite to least >

Wario Land Shake it!
Klonoa
Super Paper Mario
NSMB.Wii
Kirby's Epic Yarn
Rayman Origins

Donkey Kong Country Returns, A Boy & his Blob and Kirby's RTDL are the last 3 2D platformers i've got left to tackle.

@Wave: You shouldn't have waited this long for DKCR, it is a masterpiece!
Anyway, my favorite 2D platformer for the Wii is DKCR, hehe.

Donkey Kong Country Returns is the correct answer.

Donkey Kong Country Returns

sometimes I'd say NSMBWii, but the deal breaker ended up being this: DKCR makes the screen too big, putting less focus on DK. Also, superior multiplayer in NSMBWii just barely cinched it.
And no, I don't know why it bothers me in donkey kong but not mario (the screen resolution, that is)

Mine is probably DKCR, but I love RO. I have yet to play any of the Kirby Wii games. Since Mega Man 9 and 10 were WiiWare, I'm surprised they haven't been mentioned yet. Also, would Cave Story count?

New Super Mario Bros. Wii
Donkey Kong Country Returns
Donkey Kong Jungle Beat

@Hauchiman
If WiiWare counts, than Mega man 9 is shooting straight in my Top 5! Only losing out to Wario Land Shake it! and Klonoa. Castlevania: The Adventure ReBirth is another great retro revival worth mentioning!

@Norfair
I wait too long for everything. I'm sure DKCR will surpass my expectations and will be absolutely wonderful after playing that terrible Rayman Origins.
I'm still looking forward to Rayman Legends on the U, because in all honesty the PS3 version of Rayman in 1080p, HDMI, true widescreen and it's superior looking visuals overall completely CRUSH the Wii version. The Wii version looks awful in comparison, but when you play the Wii version on it's own and get used to it actually looks beautiful, just nowhere near or even remotely close the HD versions. Even then, Rayman's gameplay is dull, the enemie placement as Cactus Jackson pointed out is drab and completely lazy. It comes off like an annoying Floaty Acrobratic Circus show collectathon. It's the environment visuals that Wowed me, they're absolutely phenomenal during the 2 jungle and underwater based worlds. Skyward Sonta is another awesome looking stage of bunch, that had me foaming at the mouth. But really, i play games to have fun, not to sit there and gush at the graphics. I would of had just as much fun watching somebody else playing Rayman than playing it myself. everything else music aside was a let down. Time to toss this little stinker in the trash, and play me some Mega man X2 on the Wii's VC. lol

Rayman Origins also suffers from poor level design, forgettable environments and horrible music. Wario Land Shake It! and Donkey Kong Country Returns shares none of this in common.

the thing is that I agree or at least kinda see almost every problem people have had with Rayman Origins.

I still really enjoyed it from beginning to end (barring frustration end game/secret level being absurd) the 2 times I played it all the way through so it had to have done something right.

There are maybe 2 or 3 quality tracks in Origins. Just not the ones with the French-ified Alivin and the Chipmunks vocals. lol
Those get annoying fast, and when you mix in the sleeping LUM jingle the experience sound wise becomes completely grating, like a hornet raping your ear drums in Uuber over drive.

As far as 2D Wii platformer soundtracks go, i'd rank Klonoa as number 1 with it's superb atmospheric dreamy soundtrack, followed by Shake it! and Super Paper Mario. And you can't forget Mega man 9's....Mega Man hasn't sounded THAT good since MM2.

I guess I'll say Kirby's Return to Dream Land. I do love New Super Mario Bros. Wii though (the propeller suit rocks, admit it!)

New Super Mario Bros. Wii and Wario Land Shake It. DKCR, A Boy & His Blob, Klonoa, and Kirby Return To Dreamland were great, too.

Rayman Origins is too shaky for me (controls are too floaty among other things), but Legends looks way better judging the demo.

EDIT: OH, and Mega Man 9 is one of the best games from this past generation. Full stop.

Out of what I have tried, DKCR It's so fun!

I only played DKCR, but it's awesome

Playing through Kirby's Return to Dreamland and Donkey Kong Country Returns and I have to say, these both are serious contenders for my favorite.