The concept of multi-character cooperative play is hardly original, but I think this is the first time I see a skeleton and a ghost. That'd be a good starting point for a great game, and your visual style is both pretty and unique.
Unfortunately, the level design is quite bland, doing the same trivial switches and valves over and over again. Calling this a "puzzle" is stretching the term.
The only actual challenge was a little jumping sequence, but the challenge was more in getting used to the weird jumping physics.
Am I going to register on your site to play more than 5 levels, or even pay for a full version? No. Never. From the 20 year old "The Lost Vikings" to the currently frontpaged "I saw her too" series, others have done the concept better than you.