I don't see good and evil as inherently very problematic concepts. A nominalist approach to them will yield pretty useful definitions that can be further refined and discussed in different contexts.
Good and evil only make sense in a larger ethical framework, however. There are many such frameworks, and they have evolved over time a great deal -- for example, genocide is "good" in tribal ethics, while genocide is necessarily "evil" in any ethical system that claims universality.
So, if we want to discuss good and evil, we have to (1) understand the ethical frameworks that give context and meaning to them, and (2) discuss the ethical frameworks themselves. Furthermore, in my ethical system, there is an imperative to (3) find solutions that allow multiple different ethical systems to coexist in a way that is least "evil" to all parties concerned.
Incidentally, it's a very interesting if somewhat laborious exercise to read through the Bible from the viewpoint of watching the ethics in it evolve. We go from purely tribalist ethics in the older bits of the OT (yeah, which includes genocide as "good"), to eventually the universalist ethics in bits of the NT ("love your enemy," "do unto others" and so on).
(Another option is to do the same exercise with Talmudic commentary -- the same evolution is equally or sometimes even more apparent. You go from the slaughter of the Amalekites to Rabbi Hillel's "Do not do to others what you would not have done to yourself.")
(To go off on a bit of a tangent, IMO Hillel's version is a much better formulation of the Golden Rule than the Christian variant, because it acknowledges that preferences are individual, and therefore doing to others what you would like others to do to you carries a significant risk of doing harm, whereas not doing to others what you would not have done to you is a fairly good way of *not* doing harm.)