You might have read about Brawl director Masahiro Sakurai subtly slamming Nintendo's IP family on one of his Smash Dojo posts. On the topic of All-Star Mode, where you fight through the entire character lineup in order of their first appearance, he says:
When they're all lined up like this, it becomes obvious that there is roughly 6-year blank before and after Pikmin. While there have been big series since then like "Animal Crossing," "Brain Age: Train Your Brain in Minutes a Day," and "Wii Sports" it does seem that coming up with a completely new character-driven series has gotten more difficult recently.
This has been great grist for the anti-Nintendo mill, but it's blown way out of proportion. First of all, Sakurai's remarks are misleading in and of themselves. By his own admission, he finalized the roster in 2005, with the notable exception of Sonic... who was added in 2007 after a website poll. So as far as the "blank" goes, it's five years between the Pokemon Trainer (Pokemon: 1996) and Captain Olimar (Pikmin: 2001)... and only four years between Pikmin and 2005. Not a round twelve years, as he implies.
And although this isn't quite on point, Lucario first appeared in 2005 in one of the Pokemon movies, but did not appear in a Pokemon game until Diamond/Pearl in 2006 (in Japan). Additionally, the WarioWare series debuted in 2003, Wind Waker was 2002 (in Japan), Luigi's Mansion was 2001, Mario Sunshine was 2002, and of course the "modern" Twilight Princess look to the Zelda cast was 2006, so it's not like Sakurai was able to glean nothing from 2001 onward. (More on this in a minute...)
But let's see what else could have been mined for Challengers between 1996 and 2005. Sakurai himself mentions Animal Crossing (2001) which totally could have been an Ice Climbers clone with Boy and Girl, and Wii Sports (2006, but no doubt Miis were in the Nintendo pipeline well before that)... a Mii Fighter is such an obvious missed opportunity.
Paper Mario (2000, Japan) could have at least offered a supersweet stage and an alternate Mario costume, if not a wholesale Mario clone character.
Chibi-Robo (2005, Japan)... definitely a character-driven series, and Olimar's presence seems to indicate that size doesn't matter.
Ouendan (2005, Japan), represented in Brawl by a bunch of lousy stickers, could have been Pokemon Trainer-esque, with you switching between several dancing, acrobatic cheerleaders. The Final Smash would naturally unite them all.
Custom Robo (1999, Japan)... I mean, come on. Like Smash Bros couldn't use a mech.
Those are probably the six sort-of-biggies that could have been Challenger material, but we can't ignore the other games from 1996-2005 who are in Brawl in fan service form, via stickers, music and Assist Trophies: 1080 Snowboarding (1998), Sin & Punishment (2000), Golden Sun (2001), Magical Vacation (2001), Stafy (2002), Daigasso Band Bros (2004), Nintendogs (2005), Big Brain Academy (2005, Japan), Brain Age (2005, Japan), Trace Memory (2005), Electroplankton (2005, Japan), and Drill Dozer (2005, Japan). So Sakurai certainly took advantage of plenty of post-1996 games other than Pikmin, but simply did not feel anyone in there was worthy of full-on fighter status.
And furthermore, he had plenty of time from 2005 to 2007 to toss in stages and trophies and such from the games released during those two years. Yeah, he did not want to develop and balance a ton of new fighters, but he was able to borrow characters and elements from Elite Beat Agents (2006), Excite Truck (2006 in NA; we got that one first), Hotel Dusk (2007), and the new Pokemon generation of Diamond/Pearl (2006 in Japan)... which, as we see with Lucario, the Assist Trophies and Spear Pillar, was quite a bit more work than just coming up with stickers from Mag Kid.
Sakurai is selling his company short here (although technically, he was hired as a freelancer to lead Brawl development). Nintendo has done plenty over the last decade, both with and in addition to their "core" stable. Which, by the way, any other game company on the planet would kill to have even a third of the core that Nintendo draws from, so all of this NINTENDO IS TEH MARIO WHORE crap is just fanboy sour grapes.
Nine times out of ten, Nintendo is their own worst enemy.