From a modern and relatively impersonal perspective, the grounding for intuitive ethics (and much formal ethics) appears to be very shaky indeed, as the Zorblaxian alien explains here (from SMBC by Zack Weiner, full comic here):
When viewed from an alien perspective, this seems like a rather absurd metric to use to judge the value of things.
But our erstwhile web comic authors also don't see any way out of this quandry (an example from XKCD by Randall Munroe, full comic here):
Of course I realize that the source of value is not at all a settled issue within philosophy. But I nonetheless would like to be able to recommend to people grappling with issues like this (how can we ultimately base what's important on something so arbitrary/ad-hoc, and isn't this nonetheless the only thing we can possibly do?) some alternate perspectives that are at least somewhat compelling.
The most obvious tack is to try Kant, but Kant is very hard to read directly, and various philosophers have argued (successfully, in my opinion) that there are a variety of errors and unsupported claims. (Schopenhauer for example.) I'm not aware of any other approach of this type that is dramatically more accessible or with dramatically fewer potential problems.
There's also the theistic approach, but that has its own set of issues, the most difficult of which include that you have to accept that there is a deity, that essentially because I say so is a good reason for a deity even though it's not for a person, and because of concerns that deities could be evil so you can't actually abdicate your role as an independent judge of value.
So is there a clear exposition of some moral philosophy that sidesteps the webcomic angst, or a compelling defense of happiness as the source of value?