It took about 4 months for me to max out my character in The Secret World. I did everything you could do in the game solo - I didn't experience any of the group instances or the PvP zones.
The first major area you play in is called Solomon Island, encompassing Kingsmouth Town (written about previously), Savage Coast and Blue Mountain. All three zones are painted with a Lovecraftian brush. The story is compelling and the visuals are frankly stunning in their realism. In the final zone (Blue Mountain) things got substantially more difficult, requiring a re-tooling of gear and spec to perform better amongst the more difficult challenges there.
The second major area you play in is called Valley of the Sun God, encompassing Scorched Desert and City of the Sun God. This entire area is set in Egypt, and you're running through archaeological digs, desert towns and pyramids and combatting cultists and mummies along the way. This area was a lot of fun. Very Indiana Jones.
The final major area you play in is Transylvania, encompassing Besieged Farmlands, Shadowy Forest and Carpathian Fangs. As should be fairly obvious, the theme of this area is Vampires. A major re-tooling of gear/spec was required here as well which was somewhat frustrating, as it required me to re-play some previous areas to get more points/gear to implement this change. The vampires weren't particularly well done either - more often than not they had masks on and acted like they had magical blood draining abilities rather than behaving like more traditional vampires. The story was the weakest in this section as well.
Depending on what faction you choose, you would be based out of one of three cities in the game. The Dragon are based out of Seoul, The Illuminati are based out of New York, and the Templar are based out of London. Each of these cities were a lot of fun to explore and the faction-specific story lines the characters follow are very compelling and drive you to keep playing to find out what will happen next.
When you complete the faction based story (I played the Dragon faction), you're told what a good job you did and that you deserve a vacation. That's it. I was left wanting more.
I've been away from the game for seven months now and am getting the itch to go back and play another character in a different faction. I guess that speaks volumes about this particular MMO as I've never felt that way about any other one that I've played.
I recommend The Secret World. It is really well-written and the gameplay is very solid as well. Aside from the gear/spec re-tooling and the weak 3rd area I think this game is just about perfect. I hope they will add more areas in the future.