I use both kinds of apps extensively. I'm no junkie, but the engagement level from my non-readers or kids who are totally stressed by their failure to read in school in more traditional ways (and in fact often hate it) is huge, and the students are far more engaged and "into" learning on the devices. That is all I need to get them on the path to reading success, in many cases. Others of course are more complex, but here in the United States, many times kids are over-diagnosed, when in reality it was simply that they missed an important cog in the reading machine, fell behind, and never could catch up.
They've had umpteen gajillion books, and many teachers. The apps help them grow beyond their past failures in a fresh new way. Hope this is helpful. :)
For my personal learning, I think the real power of these devices is their instant accessibility to information. By this I mean...the short power up time, the many apps that provide (or organise) information, and the collaborative apps that support PLNs.
For my young Prep students I find creative apps appealing. But, I would love to see more authentic educational apps, or even apps that mirror those traits mentioned for my learning needs, but at a child appropriate level. Why not make a Zite app for children?