Alright, before anyone considers watching Code Geass, one things you should know: It fits a *lot* of anime archetypes. If you look, you could find almost anything. On to the review.
Geass sets us in a very interesting situation to begin with: a world that starts out looking somewhat black (britannia) vs white (victimized rebels/japanese). Then throw one unusually intelligent expatriated Britannian prince and a mysterious waif with mysterious powers into the mix and the story speeds up.
Some things to like about CG:
The series rapidly takes on a gray v gray moral tone. This is a nice departure for me. Some of the heroes are anti heroes that get results while others are lawful goods that have the right idea but won't do what it takes to get stuff done (lelouch vs suzaku right there). I really liked this moral balance; every side is given almost equal weighting.
Anti heroes, and we mean really anti. YMMV, but I really like it when a series takes a positively evil character, and makes them (believably) a hero. Elfen Lied is another good example for me (lucy/kaede). It also helps that Lelouch is just ridiculously smart and doesn't waste his time angsting over silly stuff like that meaningless dead civilian for very long.
Loads of twists that are often interesting. Code Geass manages to convolute its own plot into a knotted mass, but every twist (for me) was well-placed, and there are lots of them.
A mix of everything. Comedy, humongous mecha, politics. It's all thrown together and it comes out okay.
Some things you won't like:
CG takes the large ham, and supersizes it to unbelievable extremes. Zero is the largest ham you will ever see. All the dramatic proclamations, spreading of arms and flying capes really crank it up, and if you aren't willing to suspend your disbelief over that, you will be *far* too busy saying "This is absolutely ridiculous" to enjoy the series.
Some characters are kinda annoying, though YMMV rules the day. For example, I found Suzaku's attitude interesting (it was a good foil to lelouch) but infuriating - all this whining about doing things the "right" way didn't get anything done for him, did it?
Overall, I enjoyed it despite its ham overdrive, and considering how many genres it hits, most people probably will. (R1, at least.)