The calculus of rules
I voted "rules heavy; like it that way," but I wanted to clarify how I define the relevant terms. You can interpret "rules heavy" to mean "there are a lot of rules" (rule complexity) or "there is a rule for (almost) everything" (rule coverage). When it comes to combat in 3E D&D, I think both are true. However, rule coverage is a good thing, and rule complexity is the price we pay.
I like rule coverage, because it allows players and DMs to define their expectations. Is my player's barbarian a Conan-like avatar of mighty destruction, or is he a misguided savage with a pointy stick? They also define the range and distribution of possible outcomes, creating moments that are dramatic and suspenseful for everyone at the table, DM included. Does the dragon's breath weapon char the rogue to the bone, or does she drop behind that outcropping in time? Rules with good coverage allow players and DMs to exercise their creative muscles, since they help arbitrate what will happen (with what probability) when the creations of the players interact with the creations of the DM.
For a given amount of rule coverage, rule complexity determines how much of a pain it is to figure out what actually happens at the table (or in the design process for the DM). Clearly, rule complexity and rule coverage are related to one another. I would say that rule complexity trades off rule coverage with another quantity, rule credibility. (Saying that every attempted action succeeds is both simple and covers a lot of ground, but no one would buy it.)
Presumably, WotC's goal with 4E is to reduce rule complexity while maintaining rule coverage and rule credibility (which determine rule enjoyment!). Conceptually, this is no different from the research in my own field (machine learning) to develop models that are both simple and that accurately match the data. Similarly, in statistical regression, you try to find small classes of functions (rule complexity) that match all of the data (rule coverage) with minimal error (rule credibility).