I agree with the decision to not categorize choices as "simply" good and evil, nor even in a gradient - it really is a matter of perspective, and a lot of my Wardens have been, while overall altruistic, above all they were practical, which is a very gray area in terms of good and evil. There is a complexity in such decisions that transcends these concepts. It's true, and very good, that each of your companions will have their unique stance, and there is an overall argument for your actions belonging to one category or another, but I think that it's good to be able to have several motivations, and that DA:O gives you a non-black and white perspective about the impact of these decisions. Not to mention that a truly balanced world is never as simple as good or evil, the above mentioned plot choices being excellent examples of this.
As to Paragon/Renegade... this is largely the same approach. Renegade isn't truly evil, it simply shows that your Shepard is willing to sacrifice anything for (ultimately) the greater good, i.e. getting rid of the Reapers. It's not altruistic, but can you really call it evil? My impression all along has been that when he/she sacrifices, kills or abandons, it's not because he hates those people or because he wants them to be hurt exactly, it's just that he/she is so focused on getting the end result that a few lives, in the face of galactic extinction, simply does not matter. There is an argument, granted, but so much of it is subjective at the same time, given the circumstances.