It's perfectly big, and not bulky. The original gameboy, that was bulky. Games don't really look pixellated, they look great. There's no K in nub. Mario Kart DS plays better with an Arkanoid paddle than with a digital nub, not that the 3DS or XL support that. The 3DS does nothing to help DS games play better, and for somebody who was harping on how they look on an XL, I'm surprised you haven't noticed that they look worse on a 3DS.
Opinions vary. To me, the DSXL is too big to fit comfortably in my pocket, unlike my DS and 3DS, therefore, it is too big. Games look pixellated to me, by which I mean I can see the pixels more clearly. There's a space in "Game Boy". I fail to see the relevance of your Arkanoid paddle point, since they are not readily available. I find the 3DS makes many DS games play better, that's why I said it. I don't find that DS games look worse on a 3DS, which is why I *didn't* say it.
As for the issue of the 3D. It *is* something of a gimmick. Surprisingly, unlike the Virtual Boy, none of the games have really *used* the 3D in a way to enhance the gameplay. I think this may be due to the desire to make the games work just as well with the 3D turned off. And the point is, they *do* play very well with the 3D turned off. The DS can't handle the graphics of Zelda or Street Fighter. And those games are worth playing, even if you turn the 3D off, which I often do.
On the other hand, I have fallen in love with 3D photography. The 3DS is proving to be an entry drug to that world for me. (I've been a photographer for many years, but never dabbled in 3D before.)
As for backwards compatibility, all I ask is that the *last* iteration be supported. The GBC supported GB. The GBA supported GB/GBC. The DS supported GBA. The 3DS supports DS. Going further back is silly and would add unneccesarily to an already expensive piece of equipment. How many games am I going to play at once anyway? Do I need access to *every* handheld game ever? No. That's what my GB, GBC, GBA & DS are for.
In my opinion, there's a lot more to the 3DS than just "games with a 3D effect". It's more powerful and more functional than the two previous iterations of the DS hardware.