Oh yeah, the Laboratory Mutt Hunt, damn. I haven't even tried Hard mode yet, though I could give it a see. I did notice some of the challenge levels have different difficulty, when I switched a challenge and suddenly bullets and enemies were moving twice as fast!

Have finished some 29 challenges now, Speedrun 4 was indeed a breeze while I already have a couple of Mutt Hunts and Friendly Fires piled up. I'm not quite sure of how I'll be able to finish those challenges in the Harvest Yard...

vgmuseum.com has an update with awesome screencaps of Contra 4, including all the stages, the endings, and all the unlockable bonus content.  They're rich with spoilers, but it's a spectacular archive.  Check on the left-hand side under "C":

http://www.vgmuseum.com/nds.htm

"Contra is a game that combines achievement with instant gratification in a tight package." - Nobuya Nakazato

I got the game yesterday, after reading all the positive comments here, and I must say, I suck! Couldn't even get past the first stage on normal without taking a continue. And I thought Dracula X was hard... So I tried easy, which got me to level 2 at least, but I don't see how I could get any better. Back to rpgs I go

the fact that the vgmuseum can be covering any NDS games at all is kind of depressing.

Played it yesterday for the first time, and I enjoyed hearing a lot of the same classic SFX sounds..  Heck the whole game is practically a replay through the original, but somehow I don't mind since it's so classic that you just can't mess with a winning formula. 

I found them covering Yoshi's Island DS to be somewhat debatable, but I'm already pegging C4 as an instant classic worthy of finding a place in the VGMuseum.

I've never been one for speed runs in video games, but I actually did a timed run on a full, nonstop playthrough on Normal today.  On a single life I can now complete the game at 39 minutes and 25 seconds -- and I'm just dying to try it again to beat my record. :)

I don't exactly think the standard for inclusion at VGMuseum is notability.

Niiiiiice.

Thank ye.  ^_^    I'm now down to 32 minutes and 8 seconds..... but I admit to losing two lives in the process.  Haste makes waste, I know. >_<;

Careless mistakes, too, like just before the stage 2 boss, one of the blue grenaders on the top ledge nailed me.  And the other when I mistimed my jump over that tiny gap just before the Stage 7 City boss.

Now down to 30 minutes and 49 seconds.  The Laser in the base levels: what a godsent.

And I'm surprised I hadn't discovered this sooner. Seems as though the ladies have yet another gameplay advantage over the boys, other than smaller hit boxes. When hanging from a rope or vine, Lucia and Sheena can actually shift left and right to change their directional shots when aiming up. This is most evident in the Harvest Yard, when taking out the purple pods.  Probotector can do this, too, but only ever slightly; at least, his shot direction still isn't enough to hit the aforementioned purple pods.

And while we're on topic of Lucia and Sheena, does anyone else notice that their boots are a mite too big on them during the Base and Factory levels? Yet in the Alien Hive, they're perfectly proportioned with their legs.  ^_^

Completed all 40 challenges, my favorite unlockable bonus is playable Jimbo and Sully from Contra 3 US, that's awesome!

Took me a good minute associating their names with the southern accents that they were bestowed upon, when I first played them.  I was gobsmacked hearing "that" famous phrase spoken as such. o_O

Congrats on making the 40/40!

Cool, nice job. 
I'm a little over halfway, with only 22 of the challenge sessions beat so far.

Ah, right -- the Japanese release was announced recently.  Set for release 3/13/2008, the new title is "Contra Dual Spirits," a continuity nod to Contra III's "Contra Spirits."  No word yet if there's going to be any new significant additions or extras, but if there is, I'm fairly certain I'll be double-dipping.

Dual Spirits box art:
http://www.konami.jp/products/contra_ds/

IMO it's not even worth it to do all 40 unless you're a completist.  The last unlock bonus is nothing special since a sound test should come standard in the options and the bonus memorabilia art is fun but limited.