The first game is my favourite tbh. It wasn't too long, and not so complicated that even a miserable noob like me could enjoy it and figure out the puzzles without too many deaths. I finished it in 6 hours on Steam. The storytelling was quite simple, but I still found it funny. What's interesting, though, is that none of the three main characters have names in the first game. But they all get names in the second installment.
Trine 2 was good. I understand why people cite this one as their favourite. But halfway through it quickly became complicated and I had to consult guides to figure out jumping puzzles etc. I quickly became a frustrated mess every time I tried to continue on in this game. But I persevered and completed the whole game + DLC. When I came out victorious it felt like I had just completed the longest game ever. It took me 13 hours. I'm a little sad that I feel this way towards Trine 2, because the story had evolved a lot, as had the characters, and the visual were even more stunning than in the first game, and this had all the makings of a great game.
All in all Trine was a fun series, frustrating but fun, and it was amazingly beautiful and there were lots of little humoristic gems in there.
Also the wizard is named Amadeus, which meant that for the duration of Trine 2 and 3 I had this song on my brain: