Well honestly, I know it goes against a lot of people here... but I don't like gaming on handhelds for extended periods of time just because I find them very uncomfortable to hold, and don't like looking at the small screen for hours on end. Especially when I have a 50" TV sitting right in front of me. At least with the PSP or a PC you can hook them up to the TV, but you can't do this with a DS or 3DS or even Vita. I commute by car everywhere and don't travel nearly enough to enjoy the benefits of handhelds. Playing a handheld platformer for a half hour is much different than playing a handheld RPG for 3-4 hours, which is what I usually do with console RPGs...
Region locking on the platform is also a stupid move. Plus with the 3DS not doing so hot in America apparently and all the doom-and-gloom about cellphone games (the one thing worse than handheld games, at least handheld games have a workable control scheme) means that a lot of what I'm interested in may not even get released over here. At least with DS and PSP, I can import and scrape by on walkthroughs/the Japanese I remember from college without needing a new system... Sony totally had the right idea with PS3 being region free, unfortunately even 360 ironically enough has more interesting import releases

Also, I don't use the 3D when I've played on a 3DS, the gimmick doesn't appeal to me at all and gives me a headache

But that's no reason to hate the system, I only wish that Nintendo used the system's extra horsepower to push better graphics instead of stereoscopic 3D.