Do not go comparing or setting your standards for The Hobbit with The Lord of The Rings. Else you will be dissapointed.
The Hobbit and The Lord of The Rings are never the same in terms of storyline. One is a journey and adventure. Another one is a quest and a battle against good and evil.
The Lord of The Rings are split so perfectly because from the start the author has canonized the whole story into 3 books. So when it comes to making the movies, I think Peter Jackson had an easier time and clearer picture on when to split the movie into 3 parts with good connectivity.
The Hobbit itself is a book. It was not as concise and thorough compared to The Lord of The Rings. So yes there are difficulties into putting an end to a movie part.
I personally thought An Unexpected Journey started and ended quite well, very very much like how The Fellowship of The Rings performed.
My thoughts on The Desolation of Smaug is: (MINI SPOILER ALERT!)
1. The starting was okay. We can see the effort of trying to relink the audience to what happened in the first film, where we see some unseen plot that builds up the whole story. But the "12 months later" was quite unacceptable as I expected something better (what happened in The Two Tower was it started off with Gandafl battling the Balrog inside the Mines of Moria, falling down into the dark abyss, just until Frodo woke up from the nightmare he had. Simple and classy).
2. I know there are more to come in the 3rd movie There and Back Again. But the ending for The Desolation of Smaug was too cliffhanging. You see the dragon flying towards Laketown and then, movie ends. Too cliffhanging and its like hitting a low note on the verge of an orgasm (sorry for my choice of words)
3. My favourite scene would be Bilbo Baggins inside Erebor, meeting Smaug. The Desolation of Smaug has its fair share of action and fight scenes, but it is nothing compared to the epic battles that have been waged in The Two Towers.
So yes, I admit that I set the bar too high for The Desolation of Smaug. :/
But overall on its own, the 2nd film is nonetheless a prelude to the epic finale