I just watched eps 13 and 14 and they were both really, really enjoyable.
13 was the one where thunder keeps striking the village and so they think Thor is angry with them. Great commentary on religion and interpretation. I loved Stoic's line: "I don't pretend to know the will of Thor." but especially loved the final analysis: "Now if we can only figure out why Thor is angry at metal..."
14 was the one with Toothless' nemesis (the burrowing dragon). Really loved the moment where Hiccup stepped into the ravine to let Toothless save him- so he could save Toothless. Really clever moment that was both touching and followed by an awesome dragon fight.
I'm really surprised this show doesn't have a larger fanbase online- I guess it has more of a 'kid's show only' aura about it than Clone Wars does, but I think it is almost as good, and sometimes better.
I haven't seen past 14, but I'm really hoping that they touch on a bit of the Viking's history as dragon-slayers, maybe have them wrestle with some of the consequences of that? I know the show never gets too heavy, but I wouldn't be at all surprised if it went in that direction for an episode.