Trine is a fantastically beautiful platformer that, for the most part, just "works"
Well, alright, so Trine is good-looking. Is there any substance? For the most part, yes. Trine is essentially a platformer that revolves around physics-puzzles. And really, a lot of the time this just amounts to enjoyable/puzzle-solving fun.
For the most part, I would actually recommend single player over multiplayer (because you can instantly swap between the three playable-characters, making the game more fluid). You have the agile thief (my personal favorite), the gravity-defying wizard, and the strong, but less agile knight. The neat thing about Trine is that there are usually many different ways to get through/solve the 'environmental-puzzles'. For instance, you might utilize the Thief's grappling hook to use momentum to toss yourself over a tall-pillar. Or, you might use the wizard to create boxes/bridges so that you can bring yourself across. Similar situations come across in combat. Would you like smash those skeletons with gravity, sword-combat, or arrows?
For the most part, Trine was surprisingly "fluid". The voice acting/sounds were pretty satisfying, and there weren't any parts in the game that really "stuck out" in a negative manner. Because of this, Trine really 'worked' as a game. Despite all this praise, however, Trine (like most other games) is not perfect. There was one particular issue that I eventually ran into while playing Trine: monotony. I would like to emphasize that this is really just my personal 'opinion', but I did encounter the 'emotion' (or lack thereof). This, however, may be biased by the genre that Trine falls into. Admittedly, I'm not really much of a platformer-fan to begin with; I'm more of a story/immersion kind of gamer. The story in Trine, for the most part, is rather superficial. Also, as previously mentioned, I would occasionally find myself kind of just 'playing to get to the next level'.
With all that said, if I did not accentuate it enough, Trine is most definitely a 'good game'. Its stunning visuals and great physics-like puzzles make it a fluid and enjoyable experience that probably, also has quite a bit of replay value due to the myriad of different ways you have to finish every level.