I don't know, I recall the DS being very well received and everyone going crazy for it as well. But I didn't have one at that time and I don't really follow the general consensus of how things go. That said, I know that games like Yoshi's New Island and Mario and Luigi: Dream Team weren't received as well as the DS entries, so things aren't all rosey on that front. But I just look at things from my own perspective, and most games haven't done much for me. I like the 3DS but I think its games are just good, not great.
Animal Crossing New Leaf didn't feel like it added much over City Folk, so I enjoyed City Folk a lot more since it was fresh. I prefer Mario Kart 7 to DS, but feel the console versions are better than both. I haven't tried the DS Zelda games yet, but I'm interested in doing so since they tried to experiment, and though I liked Link Between Worlds, overall I still felt rehashing an old game's world was super lame. I prefer NSMB DS to NSMB2 also, but again the console games are better. Same with Mario Golf. Now I know some of these series didn't have DS entries and I never played things like the Animal Crossing DS game, but it is a part of why I haven't been viewing the 3DS as anything special.
The main area I feel the 3DS is lacking is in RPGs. It has some, but not nearly as many or the variety that the DS has. And RPGs are the main thing I'm interested in with the 3/DS, since most other genres are well represented on Nintendo's consoles. I mean, just look at all the different Final Fantasy games that were on the DS, including the first US release of the real Final Fantasy III. Dragon Quest games were also huge on the DS, and though there are some on 3DS in Japan, none of them have been released in the US. Dragon Quest VII would give the 3DS a lot more points with me, but it doesn't look like it's going to be released here. Then there are also experimental RPGs like Radiant Historia.
Puzzle games are another reason I like the DS. The 3DS doesn't yet have good answers for games like Tetris DS, Picross 3D, Planet Puzzle League, Polarium, Metoes, and others.
I guess that stuff is mostly third-party, though Nintendo was involved with some of it, such as publishing some of the Dragon Quest games in the US. But on Nintendo's side, there is still stuff like Advance Wars missing from the 3DS library. I don't think 3DS has a WarioWare title, or anything else Wario yet. The Kirby game on 3DS is very traditional, perhaps too much so; the DS has many wacky Kirby games. I could think of some others if I looked at a list.
So I guess I agree the third-party support is part of the hole I see in the 3DS library, but I still haven't been too thrilled with Nintendo's offerings. And I compare it to consoles as well, not just DS, and I s'pose the DS had some questionable software in its first couple years as well. I didn't own a DS when I got a 3DS so I'm experiencing all the DS games for the first time. And with exception of Luigi's Mansion 2, I'm finding that I like DS games better for my tastes.