Thief: Deadly Shadows' hub area is a pretty good example of the unnecessary type. But it was 2004, and you can probably guess there was some sort of "This GTA game is hot and has an open type world! Let's put one in our semi-hardcore traditional stealth game!"   I feel like that game in particular didn't need a hub because of how well the level based structure of the previous titles worked. 

Meanwhile, I'm probably going to say that the hub area in Ultima Underworld 2 is good, since it sections off the actual adventuring areas from one another and doesn't intimidate me nearly as much as the giant sprawling labyrinth of the Stygian Abyss does. That's obviously the major structural difference between them, and I think it works in the sequel's favor.  

Then there are your general headquarters that are in almost every modern D&D RPG, usually places where you store/craft your loot and talk to your companions. The strongholds in Baldur's Gate II represent pretty good examples of these, having their own little mini quests to go along with them and adding yet another layer to game already thick with content. I'm not sure what point I'm exactly trying to make here, other than "Sometimes hubs are good and sometimes they are bad", but believe it or not, there are some things that I don't have strong opinions on, one way or another. 

The hub (nexus) in Demon's Souls was interesting and well done, in my opinion.
 
It was the only place in the game where you could feel safe.

I don't have a lot to say on the matter, but I thought ODST had a great hub world that felt relatively engaging, even in comparison to its more linear individual missions.

Thief: Deadly Shadows' hub area is a pretty good example of the unnecessary type. But it was 2004, and you can probably guess there was some sort of "This GTA game is hot and has an open type world! Let's put one in our semi-hardcore traditional stealth game!"   I feel like that game in particular didn't need a hub because of how well the level based structure of the previous titles worked. 
 
Meanwhile, I'm probably going to say that the hub area in Ultima Underworld 2 is good, since it sections off the actual adventuring areas from one another and doesn't intimidate me nearly as much as the giant sprawling labyrinth of the Stygian Abyss does. That's obviously the major structural difference between them, and I think it works in the sequel's favor. Then there are your general headquarters that are in almost every modern D&D RPG, usually places where you store/craft your loot and talk to your companions. The strongholds in Baldur's Gate II represent pretty good examples of these, having their own little mini quests to go along with them and adding yet another layer to game already thick with content. I'm not sure what point I'm exactly trying to make here, other than "Sometimes hubs are good and sometimes they are bad", but believe it or not, there are some things that I don't have strong opinions on, one way or another.

@ahoodedfigure:

Just very barely relatable, those two. Their idea of a hub, where you talk to characters in between missions with static screens, is only similar at its very core. Starcraft 2 has obviously updated it since then.

And I gotcha on the detached hub. Hmmm. Let me think. Vampire - The Masquerade: Bloodlines had one kinda sorta like what you're talking about, but to be honest, I wasn't a huge fan of the game as a whole. The hub mechanic was serviceable at best. I used to really like the base in Perfect Dark for its interactions and its shooting range, but again, times have changed and rendered it a little bland and devoid of life.

Certain hub areas work all right for me, but sometimes, to make a world actually feel alive, I guess I wish there were more of them. The game I'm thinking of in particular here is Lord of the Rings Online. It really only feels like there are a handful of central hub areas, those being the major cities mentioned in the novels, when in fact the occasional outpost or two acting as a hub might be a hugely welcome change. I think they actually did try that at certain points in the game's existence, but the player base tended to stay around the earlier major hubs, which is a shame. It gives the world this eerie empty feeling when you come across a town and no one but NPC's are in it.

I should mention I greatly enjoyed Starcraft 2 and (strangely enough) the Wing Commander series' hubs. I guess that's not so surprising, considering they're very much alike.

I generally like hubs but how effectively they work absolutely depends on the circumstances. They tend to work best in larger games with many thematically disparate areas (because teleporting from a hub doesn't make the sudden switch from a desert to a swamp seem all that weird) as well as games where you always have a need for half a dozen conveniences like merchants, or a forge or an alchemy bench or item storage.

Off the top of my head, I'd say the best examples are Oblivion or the Fallouts where you are given several choices for where to set up a base of operations, so the hubs in their case feel more organic. Like they're simply spots where you've chosen to settle and make a base, rather than the game deciding for you.

I also dig the increasingly lively hubs of games like Dead Rising or Suikoden, where you can go back and see how it's filling up with people you've helped or recruited, or Assassin Creed 2's villa as it builds up with all its upgrades. The recent Ghostbusters game (not the dualstick shooter one) had a nice touch where the possessed object collectibles you found all made their way back to the Ghostbusters HQ, and you could walk around and find out where they're all living. Making hubs a bit more dynamic like that definitely gives them more character beyond simply being the designated safe zone.

Doomthief

Hubris