First of all, happy new year. For some, 2009 was the year of the Ox and 2010 will be the year of the Tiger. For me, 2009 was the year of PewPew, and 2010 will be the year of PewPew 2!
In 2009, most of my time was spent on creating the engine and getting to know the iPhone. Now that the engine is done, I am almost exclusively working on the content: I am creating tons of new ennemies and even more levels.
I say "almost exclusively", because I actually did improve the engine. I did an important (though obvious) optimisation regarding the collision system (Chromatic Conflict is smoother now because of that), I made explosions luminous, and I am in the process of adding sound effects.
The light added to the explosions is just an expanding texture (not even billboarded) whose transparency increases until it becomes totally transparent. It's simple, but it looks real good, I can't wait to post a video.
The sound effects are handled with OpenAL. OpenAL enables you to specify the relative position of the sounds, though I don't know yet whether I will use this feature or not. Basically, this feature allows you to changes the volume of a sound effect, depending on the player's position. For instance, the nearer an explosion happens to the player, the higher the volume of the explosion will be. What's even more interesting is that the volume of an explosion happening to the left of the player would be higher in the left earbud than in the right earbud. You can create other effects, such as the doppler effect, but that would be overkill for PewPew ;-)