Relaxing, with a bit of challenge.
There's something about PixelJunk Eden, and its expansion Eden Encore, that draws attention to it. The art style is unique, and it turns heads. It's a simple enough game that people are willing to stop for a few moments and try to figure out how the game works; after a few moments, it seems simple. Pop pollen bubbles, grab pollen, tag pods, get more plants to grow so you can progress in the level, grab the glowing spectra to finish it. People who have never played the game pick up the controller, and then they start to play, and they get it.
The atmosphere is also a good blend of trippy colors, flashing lights, subtle animations, etc. A few screenshots and videos give you a glimpse into the unique style that is PixelJunk Eden. The sound mixes in well, it's got some foot-tap-worthy tunes in it, and that in itself is often an accomplishment in a video game.
Most people begin to complain about challenge. For a relaxing game, the challenge seems unnecessary; the game is more about the experience of bouncing around grabbing pollen, growing plants, etc. As a "hardcore" gamer (whatever that means), I found the timer to be a nice change of pace from the easy bouncing and swinging the rest of the game provides. Getting one or two spectra is rarely a challenge, getting four or five becomes an interesting mix of race, skill, and resource management. And, Eden's most recent patch removes the “difficulty” by allowing players who run out of time to start from the last spectra they collected. It's a good compromise for those complaining about the difficulty.
Learning and experimenting take this game's challenge and turns it into something fun in its own right. Learning how to extend your timer, by popping 5 pollen “prowlers” in a single jump, learning to save the big “time points” for when you really need them, or racing to get the next spectra to fill up the timer are skills that you develop over time. And, the fact that each level has its own unique mechanic, like gravity swapping, teleporting pods, new enemies, and flowers that launch you skyward, the ten levels in the base game, and the five in Encore, provide more than enough enjoyment for the money. If you have a PS3, this game is like an art piece; it will stop people, and make them think about what is going on.