TOOTHLESS ISSSSSS BACKKKKKKK! This is a whole new reason for you to fall in love with dragons again! The first part teaches you about tolerance, love, and also synergy. The first movie show you if you believe in something and pursue it, good things will come from it. People will learn to not only accept that you are crazy, but also succumb to the fact that something awesome/crazy will comes from all that persistence. At the end of the movie, Hiccup managed to make dragon and vikings come together and work as a community (spoiler!)
Everything about the chemistry of Hiccup and Toothless makes you want to own a freaking dragon! The on-screen chemistry keeps giving you the jab on your bone which makes you go AWWWWW. The main character and the dragon seems to have lots of on screen time which allows you all to understand the bonding that they have and also what makes them so compatible. The types of dragons and also the ALPHA dragon makes you wonder what it is to live in the world where dragon existed. Kinda feels like Skyrim (sorry I got excited). There are many different types of dragons and also some fantastic weapon that wielded by Hiccup which makes the whole experience very refreshing.
With the first movie seems like a good movie for a kid to watch, the second movie seems abit more dark and also sad moments. Death in a fairy tale however much I like them, seems like it is going to give kids nightmare. Besides that, Hiccup's mother character did not have much time telling us how she learn all the skills to unlock a dragon's talent. She disappear for 20 years but then nothing of her is well know except that she is Hiccup's mother and she looks flawless. That is about it. No back story nothing, and the Alpha Dragons doesn't seem to have any explanation how many of them left. I wish there are more with different skill set instead of only ice.
How To Train Your Dragon 2 still fares better than the first movie which now shows much more action compare towards the first movie which is understandable. Basically, the whole movie is really fun for me, lots of laugh and also sadness moments for me. Aside from that, I am pretty sure you will enjoy this if you enjoyed the first movie :). Sit back, grab some popcorn and enjoy the flight!
TL;DR: Dragons and vikings, lots of actions, some down moments, and be prepare to laugh and cry at the same time!