Are certain types of projects more or less desirable from a programming standpoint?

Definitely! I'd rather clean the floors of all the Orange Line trains with my tongue than write a cell-phone game.

From a purely geek-chic standpoint, every programmer has their own preferences as to what's a desirable project and what isn't. Some of the guys on my team would love to optimize low-level microcode on the PS2, and some enjoy high-level systems architecture. Others geek out on developing tools in the latest scripting language, and still others are all hot for the [unmentionable hardware capability] in the [next-gen console which may or may not exist]. Personally, I'm in it for the visuals-- if I can work with talented artists to make a game with beautiful 3D graphics and animation, then I'm sold.

But in the end it's the game itself that ends up on the shelves, so the most desirable projects are the ones that allow us the chance to focus on making a great game. These are the projects in which the technology requirements are very challenging but achievable, the visual aesthetic is distinctive, and the gameplay is innovative, fun, and open-ended. That pretty much describes every project Irrational Games has ever undertaken.