As with most people who are in love with the movie, I had some high expectations for the series and was worried that 'Dragons' would end up like 'Kung Fu Panda' and 'Penguins' (which I understand is geared towards kids, but it kind of ruined the franchises for me). Luckily, the people involved with the movie seemed to want to set this apart from those two. Instead of airing it with Nickelodeon, DW aired it with Cartoon Network, much to my personal dismay. As the series progressed however, I found myself (mostly) agreeing with their decision because of the seriousness of series.
Just a real quick overview of the series in general: it doesn't really seem to have a set time of where it begins in terms of the movie. It does however look like it happens a little after 'Gift of the Night Fury'(still doesn't clear up the time line) because the teens know that dragon eggs explode. Next, the quality is not as great as the movie, but that can be chalked up to a limited budget so don't let it distract you too much. Lastly, it's main focus is on the teens and their dragons trying to help Berk get along with its new residents. While most people are willing to cooperate, there are some who aren't willing to let go of grudges. It also expands on ideas that were mentioned in the movie and digs deeper into the characters.
One thing I like about the series is that it's easy to see how the teens grow in their relationships with both their dragons and each other. At the end of the movie, we see the teens begin to respect Hiccup and the series expands on that. There are some exceptions, mostly with Snotlout, but when the situation calls for it they'll listen and be there for him. Next there's the awesome relationship between him and Toothless. In almost every episode, it's obvious that the pair have grown close and will do whatever it takes to protect each other. In the episode 'The Terrible Twos', the pair go through a small split that results in Hiccup stranding Toothless in their cove. In the end however, they make up and realize how important it is to listen and trust one another, which continues on for the rest of the series.
There's also the focus on Hiccup and Stoick's family relationships and conflicts. 'Gift of the Night Fury' offered a slight glimpse of them trying to work things out and the series picks up from there. The first is when Stoick gives Hiccup the old dragon killing arena to use as a Dragon Academy, showing that he's willing to trust his son with responsibility. In 'Alvin and the Outcasts', Stoick is generally worried about Hiccup when he finds out that Alvin the Treacherous, their greatest enemy, has taken his son and in a later episode titled 'We are a Family: Part 2'. Also, Stoick is willing to embrace his son's ideas by accepting his own dragon in 'How to Pick Your Dragon', something he claims earlier goes against their Viking traditions. During this episode, it seems like Hiccup's efforts do not work due to his father's stubborn and Viking-like attitude, but at the end it shows that Stoick does listen to his son (though he'll deny it). The greatest example of their improving relationship is in 'Portrait of Hiccup as a Buff Young Man'. In this episode, Hiccup goes on a small quest to prove to his dad (and himself) that he can be the kind of Viking they think he should be. The challenges in this quest (which even Stoick took on) are only solved by Hiccup being himself, proving who he is to both himself and his father. The end of the episode shows the two standing side-by-side with Stoick's arm on Hiccup's shoulder, eyes filled with pride.
And let's not forget the Hiccup and Astrid romance here. Surprisingly, there's very little focus on that. Instead, the focus is on them becoming good friends who offer each other advice and brutal truths. When Hiccup is faced with a conflict he can't solve on his own, Astrid is one of the first people who offers to help him. In return, Astrid sticks by him to make sure he follows her advice and keep him from getting killed (which happens quite a bit). There's a few glimpses of their blossoming love: when they huddle close together for warmth in 'Animal House' only to back away from each other embarrassment, Astrid giving him playful punches on his arm, and when Astrid grows jealous of Heather in 'Heather Report: Part 1/2' because the other girl is stealing Hiccup's attention (there's a bit more to it but don't want to spoil it from here).
So while the series has some of its amazing moments, there's also some parts that drag it down. I won't dwell into those though much because those types of matters depend on your opinions. I can go on about the series, but I'll stop here before I give everything away.
To wrap it up, 'Dragons: Riders of Berk' is a very good series that helps strengthen (and sometimes weaken) the franchise in general. It's a bit more serious than DreamWorks' other spin-off series, but it works well due to the nature of the movie and can be off-set by its comedy (also sometimes weak). For those of you who can't get enough of 'How to Train Your Dragon' and can't wait for the second movie, this series is great for you. Besides, I heard that this and the next series, 'Dragons: Defenders of Berk' which will premiere sometime in September, deal with events that occur between the two movies so its probably good to see what happens.