BonusLevel.org comes up with an intriguing idea. Flash-based puzzle games that once you're finished playing, you can create some of your own levels to add to the gestalt. Community created gaming is a great idea, and with a simple enough level designer, and of course the differentiation process of having registered users vote for which they like, it offers near-endless amounts to play.
BonusLevel is still reasonably young, and only has two games on offer. But it's going to need some serious improvements if it's going to catch on. Not least the music, which as I type is forcing me to chose between two career paths: serial killer or kitten stomper. And... muted. The two games are CoBaCoLi, involving a sort of pool on ice game of knocking coloured balls around until they bump their colour-coded wall, while protecting the cue ball fro touching the edges; and BLockoban, a Sokoban-inspired puzzle game sliding blocks to reach their targets.
Let's get CoBaCoLi out of the way, as disappointingly it's pretty poor. Perhaps the core game has some potential, but currently the painfully slow movement and poor sense of aiming spoil the fun, which is already hindered by some dramatically awful presentation. The spinning screen between levels makes my eyes hurt, and I really don't need to see the instructions interrupting every single level.
However, BLockoban is a much better affair. It's a familiar puzzle style, and one that's always fun. And here the presentation is excellent, the boxes moved in the most statisfying way: clicked on by the mouse, and then flung in the direction you choose. I love flinging stuff. It makes me feel like a wizard. Again, there's room for improvement, like the game being able to recognise when you've lost and automatically offering a restart. However, it doesn't share Cobacoli's irritating instruction screen or head-breaking spinning ugliness, but instead a nice, neat cartoony presentation. So long as you turn the dreadful music off.
So, in short, play BLockoban lots and lots - if you get stuck on the official levels, you can always jump into the user-made ones for a break. If you make anything especially great, tell us here.