Not really. Perhaps it's the lack of memorable characters. Mario Kart DS featured an entire cast of fan favourites while games such as Diddy Kong (who?) Racing featured the apes from the Donkey Kong franchise. Who likes playing as an ape all the time? I'd rather be a certain popular Italian plumber.
Even games such as Need for Speed Pro Street and Race Driver: Create & Race, where graphics and realism are two equally important selling points, are hard-pressed to be as memorable like Mario Kart DS. There's one thing of creating very nicely rendered cars and there is another matter of viewing the same cars through the small screens on the DS.
In the words of the late Joker (Heath Ledger), "Why so realistic?"
And then there are the mediocre titles, which do nothing to provide a better video game exprience. Hot Wheels: Beat It may be sitting at the better end of this low spectrum but don't be fooled by the initial FMV sequence as the in-game audio is horrendous. All the crackling and popping will have you thinking that your Nintendo DS speakers have gone bust.
Go down one level and you'll have shovelware. I can't really think of any except for Homie Rollerz and that game is just plain drivel.
So, with racing games being as they are on the Nintendo DS, can we expect a better game to that of Mario Kart DS? Maybe perhaps a sequel. Now I'd buy that!