For fun, I googled "seven deadly sins of design," to see if there were some better lists pertaining to design in general. Got nowhere with that, but then I tried "seven deadly sins of architecture," and found a good list from a bunch of grad students at Washington State University:
1. Fatness
2. Separateness
3. Messiness
4. Bigness
5. Sameness
6. Flatness
7. Vagueness
The only one of these that I have trouble applying to modern golf course architecture is vagueness.
The most important of these, which Darius didn't really include, is BIGNESS. The trend I've noticed the most over the years is that all the award-winning courses of recent years are built at the biggest possible scale. My courses are as guilty of this as any; that's one reason they've won a bunch of awards. But, I'm convinced that bigness is ultimately a bad thing for the game of golf.
We have to maintain much greater areas of ground than the old courses did, because there is no overlap between holes -- no parallel fairway where you can find your wayward drive. Courses are so spread out that the maintenance regime of the day involves 15 crewmen, each with their own vehicle. Environmentally, this has all been sold as a win, because the golf course is maintaining +/- 100 acres of "habitat" ground that is a benefit to the community ... but ultimately a drain on the golfers' pocketbooks.
Some pieces of property [like, anything in the Sand Hills] have a big scale of their own, and it would be crazy to try and design a "small" course in a vast landscape. But the success of those courses has led to almost ALL modern courses being designed at a big scale, whether or not it's appropriate to the site.
You could lump 7500-yard tees into this sin as well, but they are only a part of the problem.