Greyhawk either benefits from or suffers from, depending on what you want in a setting, a lack of development over the last decade, and, IMO, has managed to remain less of a 'kitchen-sink' setting as a result. It ends up feeling more coherent, and yet also being more easily adapted to be 'your' setting. (I'm playing the Freeport Trilogy right now, with Freeport set in the South Olman isles, and much of the city set up around Sueloise influence, with Wee Jas, Lydia, Kord, Norebo, Osprem and Xerbo as the nameless gods of that series. I mention this on Greyhawk lists and I hear, 'cool!' On the WotC boards, suggesting making a tiny tweak to another popular settings leads to flames, nasty private messages, and the moderators being spammed with complaints that *you* have been causing problems!)
If you want samurai in your game, the Realms has absorbed the entire Kara-Tur setting, along with several other settings, such as Zakhara/Al-Qadim, and Maztica (which was actually designed as part of the Realms, so it wasn't 'absorbed' really). Almost anything you could want to play, you can find somewhere in the Realms.
With Greyhawk, it's a more coherent setting, with less stuff 'absorbed' over the years, and you might find yourself thinking less of 'how can I play a Samurai' and more 'how cool do those albino wolf-women from the Frost Barbarian reaches sound?' I find that drawing inside of lines channels creativity in ways that just playing whatever the heck I want, and expecting the setting to make room for me (as Spelljammer and Ravenloft where designed to do), does not. Dark Sun, even more than Greyhawk, is an example of a setting that very sharply constricts player choice to setting-specific race/class choices, and yet only promoted creativity (again, IMO) by making the players 'draw' their characters within the setting-specific 'lines.'
Still, not everyone wants any lines on the paper, and Greyhawk will not be the setting for them.
Number one point;
Greyhawk is the only D&D setting with a diety of *beer.* (Wenta, the Alewife)