Angkor Wat is to Cambodia what Macchu Picchu is to Peru. You just can't go there and not see it. Though I'm glad I did my 5-6 Cambodia trips in the 1997-2002 timeframe and would likely be shocked and a bit disappointed in spots, though pleased about others (on my first trip the Khmer Rouge were still holding territory, for example).

Cambodia is kind of a rough first place to go if you haven't been elsewhere in Asia, but I'm sure now it's a lot tamer than it was. "Off the rails in Phnom Penh" by Amit Gilboa is a good read about all that if you can find it.

Part of the case for Angkor is that, while it's way too crowded and "ruined" in many ways, that won't be getting any better absent something like another big war. So see it before it gets even more crowded and they finally open the McDonald's. I remember having the overlook peak to myself and having to share the main temple in late afternoon with less than a dozen people or so in early 1997.

You don't want to need health care in Cambodia. I once did need it (food poisoning) and it was nightmarish.

The FCCC in Phnom Penh is an absolute must to visit.

I got to Sihanoukville before the massive development started and got to see the Independence Hotel in ruined glory (mines were a big concern, though).

I suspect that PP could be pleasant in some respects because so many people bypass it now for Siem Reap. Other outposts besides Angkor, PP and Sihanoukville are probably far less changed over the years.