My friend Kari posted a comment in reply to my EVE post. Not talking about EVE, but instead about Age of Conan which I'd mentioned in that post. Her comment:

AoC doesn't have the population to be anywhere as fulfilling as it should be. Gorgeous game, fantastic PvE but no population to drive the economy.

And trust me, if you want to go anywhere near city-building, you need A) a population and B) an economy.

AoC is a large-guild-only game. A crack team of 8-12 elites will make it to 80 very quickly but will NOT be able to progress a city beyond the first stages.

Her comment is both true and not true - depending on what you want out of the game.

As far as "no population to drive the economy", I'm not sure. The population certainly seems very high on the server I play on (Cimmeria). There's always a lot of people around. Whether or not the economy is "working" is another matter; I'm too low level to notice. Then again, does any MMO have a super functional economy? They always seem a little borked to me anwyay. The server merges did massively increase population on most of the remaining servers.

The city-building bit - well, yeah. A city implies a lot of people, so yeah, it takes a large group of people to build/maintain a guild city. I think that's intrinsic to the idea of a city in the first place.

As far as other things to do, to make AoC worth playing, well, for me, I want "quick and dirty", "get in and get out" type of action. I can log on, do a couple quests, or go to a zone and do some random PvP and then log out as needed. That's really all I want out of a "secondary" game right now. I don't have enough time to "really seriously play" 2 games - and EQ2 is definitely my primary game, as I play with my wife, and the fun and awesomeness of that just can't be beat! So basically I need a "secondary" that's playing and "stoppable" easily, while still feeling worth it when playing in that mode. Basically for me, right now, that'd be either AoC or World of Warcraft. Possibly Warhammer also, but I really don't know anyone else playing and I at least want the option to play with a friend or two when I have a tad more time.

I do have another friend that's playing AoC at the high end though. He's got 3 (or maybe 4) max-level characters and they're all guildless and he raids on them! Pickup raids are super-commonplace in AoC, and it's no problem to participate in that aspect of the endgame content without a large guild - indeed without any guild at all!

So, in short... AoC's playable solo or small-group, depending on what you're wanting. But, yeah, city building, yeah, that's for larger guilds.