Depending on when you played, The Hollows wasn't to be considered a "failed zone". For a good while, it was almost certainly the next zone players went to from AP because that's where the initial AP contacts sent you to talk to the officer in charge of the zone. Sure, later on players could just DFB until they were in level for Posi, head to Steel Canyon and go from there after the TF, but to say that The Hollows was a "failed zone" is a bit of a stretch. They even added creature comforts like a field hospital and a trainer so players wouldn't have to take the death train to the AP hosp to train up since Ms. Liberty was the closest trainer previously.

As for other zones that are essentially re-paints, while it serves as an efficient method of re-purposing content with slight modifications, efforts along those lines tend to smack of laziness and would very likely receive negative feedback from the playerbase, especially if it is very obviously just a re-skin of something else.

[b]Post-apocalyptic zone[/b]: Boomtown is a great example of a hazard zone that had a solid story behind it but no one really seemed to play through anything there other than to get the exploration badges required for a specific accolade or if you wanted to fight Babbage outside of the Syn TF spawn for the badge. I was just as guilty of it as much as the next player, but once you've played through it once and remembered the struggle to navigate through the rubble of the zone to get to an elevated mission door, you tend to find other zones to play in that aren't as frustrating for someone with just superspeed. Now, if SS could run up walls and such... it wouldn't have been as much of a hassle, if any at all. That being said, I do enjoy post-apocalyptic content and wouldn't mind seeing content that's worth re-visiting after a single play-through.

[b]Opposite World[/b] with oppressive supers might seem a bit too much like Praetoria and the Going Rogue content that it could lead to legal issues, particularly for a game that's viewed as the spiritual successor to CoH/V. After all, CoT isn't CoH/V2. That's not to say that it can't be done or hasn't been done, but I think it would have to be done carefully. Maybe if it was truly Opposite World, where supers are the normal population and people without powers are the minority, now that might fly (no pun intended).

[b]You Are The Villain[/b]: I would personally rather wait until I can play a real villain from an expansion release from MWM, although if they had a storyarc that alluded to the next release being about playing a villain, that'd be super (again, no pun intended).

[b]Giant Monster World[/b]: For a period of time, I was THE giant monster guy on our server, it seemed like. But part of the fun was getting people together ad hoc and hunting GMs across their respective world zones. I have mentioned instancing in a separate thread that also included GMs as an example, but it was more related to raiding and the controls required to manage one when it comes to dissenting elements versus a world boss situation. This isn't a bad idea, per se, but I think the instancing portion takes away from the environmental threat of the GM in the actual zone(s). Why bother having them in the zones if players can just go to an instance and fight them? Players wouldn't then seek them out in the zones, and would likely only serve as a minimized problem for a new(er) player who happened across them unknowingly.

As for a zone suggestion, I wouldn't mind seeing an underwater zone or even a series of zones related to the four elements. Maybe it's to boost or enhance your current powers or even recharge your fire-, air-, earth, or water-power(s) that have been weakened by a supervillain's actions from a previous storyarc. Or maybe the air content could involve the Aether Pirates trying to fill the skies with poison, and the fire content could be a pyromaniac's dreams that you need to extinguish, and the earth content could involve spelunking into the depths of the earth to relieve pressure to prevent an earthquake, and the final water content could take you to the lost capital city of Atlantis where you have to fix their shield machine that keeps their city safe from the crushing pressure of the ocean. Maybe you learned a little something along the way from each of those other pieces of the content that enables you to fix the machine; a shiny tech-widget from the Aether Pirates' ship, a precious stone formed from the geological forces of the earth, the imaginative and possibly illuminating power of dreams, etcetera. I think that'd be a good way to tie it all together.