I just finished the demo for Trine on Steam and I am sold.

Trine is a lot of fun at the core and looks as though its replay-value will come from one of the best aspects of the game:  Solving the puzzles and challenges at your own approach.

The game takes 3 characters that all have somewhat conflicting personalities and meshes them into one.  A thief has snuck into a castle and attempted to steal a crystal, not knowing that it is enchanted, and becomes literally attached to it.  A dazing wizard who awakes as you are introduced to him, lying by his spyglass is then met and makes his way to the crystal as well.  He is surpised to see the sultry looking assassin there as he is a "ladies man" (supposedly) and approaches as such, getting stuck as well.  You are then introduced to the Warrior who for some reason is practicing his sword skills on a box.  He makes his way there to protect the treasure.  All 3 are glued to the enchanted crystal and mesh into 1 cohesive hero.

This is the fun part.  You are let loose in the castle which is being overrun by, what else?  Undead.  There is a lot of platform action going on here and the puzzles, at least in the demo, are nothing that hard but were very fun and leave a lot to think about what you might see in the full game's later stages.  The action is smooth and you can switch classes on the fly.  I found that in combat I was killing skeletons faster by swinging twice as the warrior and swapping to the assasin quick and firing a quick shot of my arrow out.  Jumping took some getting used to as it feels somewhat erratic but it works well and you can jump off of most objects no matter how steep of an angle they may be at.

The abilities are limited in the demo but you still feel as though you have many, many options for any situation.  Creating boxes to crush skeletons or to reach a higher platform is great.  If magic isn't your thing you can always use the grappling hook to get up there and fight with your bow.  The warrior, at least in the demo, is SOL on moving objects, but in the full game, as you level up, you can unlock abilities to allow him to do more such as lift, carry and throw objects.  I really only found myself using the knight when there was combat or projectiles around, but really, he will have a lot more use than his type-cast roles in the final game.

Trine is smooth in its action and addictive in its progression.  The demo feels as though it ends upruptly and that somewhat feels like you've been cheated out of more time with Trine but it really isn't so.  It is simply the fact that Trine is so fun that you will likely always wish for more; that said the demo feels just right as it gives you plenty to enjoy and leaves you wanting more, exactly the point of a demo.

All in all, I can say before playing the demo I was already hooked by the gameplay trailers, but after playing it, it is a done deal and I can't wait to get the full version, likely on a console :)