The game is obviously lackluster, but that's because it's a portable version. For what it's meant to be, it does a superb job.
Which is fair, maybe I am focusing too much on the verbiage, but if I were to write to Sakurai "You know, the 3DS version if kind of lacking", I feel like it would be an inappropriate way to describe the content of the handheld version. I am not saying Smash 3DS is perfect, or that there were simple additions it could have used, but I was more than satisfied with it is a product personally. To describe it as lackluster in it's own right I feel doesn't paint an accurate picture.
Now, for those of you who saw the Nintendo Direct, the Wii U version will have TONS AND TONS AND TONS OF CONTENT. Probably because 1) It's a home console, 2) they had more development time, and 3)They might have had a bigger budget for the home console version.
So Smash Wii U looks to have more content than Brawl so far, and THAT is a fair comparison to me because they are both home console, blockbuster video games. The 3DS one in comparison might seem lacking, but honestly, the 3DS system itself could be argued that it's a "bit lacking" as a handheld. Just because 1 or 2 single player modes aren't in, which I presume you would not spend most of your time playing anyway, I feel is moreso cherry picking, which is fine, I just don't want the negativity to stop you from enjoying the purchase you made to the fullest.