Obviously, the big things are the same for both type of movie: you want to create memorable characters and a great story, and that's always the number one priority. But there are a couple of subtle differences:
The biggest difference (to me) is that when you board a CG movie, you have much more freedom to move the camera around and use camera moves to tell the story. When boarding 2D you always have to be conscious of the limitations of the backgrounds as painted stills, whereas in 3D the backgrounds can be built so that the camera can move through them, show them and explore them in their entirety.
I wouldn't say that one version is better than another, they're just different - they have different strengths and different weaknesses, and you have to be aware of them and consider them while you're storyboarding.
I recently watched the film "The Good, The Bad, The Weird" on Netflix and I was struck by the opening, which uses a series of long camera shots to set up the tone of the movie and the main character. It's a good example of the type of thing that you could do in a CG film but would be impossible in 2D.
Here's a version (without subtitles, unfortunately) and take a look at how the opening sets up a certain unique tone for the film (music is used well to do that too).
Once we get on the train, we are following the main character, who is pretending to be a vendor selling food on the train. The film takes place in a unique setting with a strange array of characters and I love how this tracking shot gets us used to the unusual setting quickly. I love how the camera tracks with him but will tilt and adjust the fielding along the way to feature different characters (like the colorful lady and the masked bandit). The film takes place in Manchuria but has elements that concern Korea and the Japanese Army - both of these aspects are introduced in passing (through the man with the Korean flag and the soldier pursuing him in the Japanese uniform) as he goes along, and all the while he's calling out that he is selling food. The fact that some sort of political drama is going on, and yet the person we're following doesn't react to it or get involved in it tells you a lot about his character, as does the moment when someone actually starts to rise up, saying they're interested in buying food - and our character pushes this potential customer back down, rudely - suddenly we realize that he's not really selling food, that it's a ruse and he's up to something else entirely. The technique of following him from behind is a great technique - it makes us intensely curious to see his face, and I love the way this whole shot is staged because all the information we get about him makes us very interested in what he's up to. And when we do finally see his face it has a great impact and punch to it. I also love the end and the casual way he shoots the last person as a sort of period on the whole thing....every one of his movements is very invested with character, personality and entertainment.
I would say the other difference between storyboarding for 2D or 3D is that there's more subtle acting that can be done in CG - it's much easier to do a scene where a character just lifts an eyebrow slightly, or just raises their lower eyelids for a moment as an acting beat. In 2D when the characters have to be drawn, we tend not to board such subtle acting, because it can be too difficult to do in drawings, but when the characters are built and rigged in the computer, the animators have a much easier time creating subtle shifts on the face and body to indicate small acting beats.
Again, neither way is superior, just different, and as a board artist you had better know the limitations and strengths of the medium you're boarding for.
The other small difference that comes to mind is that in 2D you can populate your boards with different characters anytime you want - if you invent a new character for your sequence, it's no problem - an animator can draw that character without much advance work being done (other than a design being worked out for the character). But in 3D, each character needs extensive lead time to be designed, built and rigged, so you can't just add characters as you storyboard. You have to be judicious and careful about that aspect and it influences how you approach things and solve problems.
There are some technical issues as well to think about as you board, depending on what is possible with the technology at the time. Years ago, when I was working on an early CG film, there was a mandate that we couldn't get the characters wet, because that would require building a whole new "wet" model of the character which was prohibitively expensive.
On "Tangled", the directors (Nathan Greno and Byron Howard) were always very careful not to tell us board artists what we could and couldn't do in the CG world. They always said to us, "just board it the best possible way you can, and we'll figure out a way to make it happen". And that's just what we did. The technical people on "Tangled" were amazing and did an awesome job of accomplishing every insane idea we threw at them. I have no idea how they did it but they are spectacular!
I promised to share some more drawings with you but I don't have much stuff on my home computer to choose from. Maybe when I'm back at work next week I can find some better stuff. Anyway, since we're looking at a fun action sequence already, here's some drawings I did of Rapunzel confronting some surly thugs in "Tangled" that I did. Man, those thugs were fun to draw....
Here's another piece I did from later in the film, with Flynn and Maximus punching each other, then getting busted by Pascal, trying to get on their best behavior, and failing. I gotta say, I've never drawn a guy putting a horse in a headlock and getting ready to punch the horse in the face before, but it was fun to do. That's what I love most about my job, you never know what you're going to draw when you go to work each day.
These sketches are all pen on paper with tone added in Photoshop.
I'm very proud of "Tangled" and I feel very gratified that it set a new record for an opening day in November! Also, I'd swear I read somewhere that seeing movies about boy wizards gives you eye cancer. But I could be wrong about that......