My theory on why a live-action version of How to Train Your Dragon exists is that DreamWorks Animation/Universal doesn’t want to lose their license to this profitable franchise. Rebooting the series with a live-action adaptation, rather than letting it go, makes business sense.
As a fan of the original series—and having covered it extensively—I still find it hard to accept a new actor playing Hiccup. Mason Thames does a decent job in the role, and Gerard Butler is excellent as Stoick, a role he seems born to play. However, the supporting cast doesn’t capture the humor and charm I loved in the animated versions.
For instance, Fishlegs’ (Julian Dennison) relationship with Hiccup feels less defined. Snotlout (Gabriel Howell) doesn’t provoke Hiccup as much, and The Twins (Bronwyn James as Ruffnut and Harry Trevaldwyn as Tuffnut Thorston) come across differently. While the performers are competent, their roles lack the comedic impact and screen time of their animated counterparts. As for Astrid, Nico Parker doesn’t quite match the fiery presence America Ferrera brought to the role.
Everything that’s once animated in How to Train Your Dragon is now brought to vivid real life in the teaser trailer released a few days ago. Toothless looks terrific and 
As for the original material, there’s good news! Cressida Cowell announced a new series, where Hiccup and gang go to school. In this series, the kids have to deal with other threats, and at time of writing, only the book cover has been revealed. Autographed editions are available to pre-order through Waterstones (UK) 
Available on 
By Ed Sum
book. The only difference is in how much material is available from these 5 to 8 min featurettes versus a 175-page book.