I think one of the major purposes of the comic medium is to find new and interesting ways to show motion and movement without actually having it. Motion comics are fine I guess (not really my cup of tea, but whatever), but I do think we should come up with a different name for them.
I'm guessing you mean like Marvel motion comics? Those are boring. I would rather watch an x-man movie, one of the cartoons, or... actually read the comic books. But there is this german motion comic online done in flash.
The background sounds/music are really well done - doesn't sound cliche, cheesy, or anything like elevator music. Its grungy art style really fits the medium, or at least is a refreshing change from the typical uber clean motion comics. There are no speech bubbles, but sound effects (like tapping fingers across a table, or screaming) have dynamic text to them. I suppose there isn't really much in the way of actual dialogue. The story is more so showne to you than anything else, as it happens. There are sequences of actual animation (if I remember correctly - I found it a couple years ago, and checked it religiously for one month before I lost the bookmark). If I ever find it again, I'll send ya the link.
Kimecan is fantastic. It gives the illusion of motion while remaining a true comic. Each page has a series of panels. Sometimes the graphics on a particular panel change. [link]
Lastly: Homestuck is a motion comic, in my opinion. Typically, each page represents a panel. Other times, it's either something interactive, or a jump in animation quality. It is popular with kids and hipsters... for some reason.
I love the idea behind motion comics...but the execution is still far from being perfect. It reminds me of the days of Reading Rainbow and other PBS series where they demonstrated pages from illustrated books with a voice over and a bit of moving images. They weren't perfect, but they entertained for a few minutes. Motion comics try to be something bigger than they are, and after a few minutes, they become a little daunting and, I hate to say it, boring. I rather picture images in my head when listening to the old radio drama than seeing still images with special effects. Either leave the images still, no voice overs, or go fully animated. There is one "motion comic" that appears better than all others. The cinematics from the dlc of castlevania. They just seem to work, and I still have not been able to diagnose why.
Most aren't very good. There are a few however that are good. I think the best way to do motion comics is like how DC did the cutscenes for DCUO (which are really more like high quality animatics than motion comics). Here's an example: [link] I think the thing that makes motion comics work better is when then they don't have the speech bubbles. Keeping the sound effects, when they add to the art, is a good idea but speech bubbles in a motion comic with voice overs don't really serve a purpose other than telling you you're watching a comic.