A couple of people were asking about this so heres a description of gameplay fom the main site:

Create Your Own Hero
Choose from hundreds of different powers and design your own unique costume.

Fight Evil!
Confront super villains, aliens, madmen, criminals, and other fearsome foes. Take on personalized missions and rid the city of several different evil organizations and hundreds of individual enemies.

Form Your Own Super-group of Heroes
Band together with other players to fight evil and become the premiere hero group in the city!

Explore the City
Explore the skyscrapers, slums, sewers and streets of Paragon City, a sprawling online metropolis that offers unlimited adventures and countless surprises.

Live the Story
Become an integral part of twenty different ongoing story arcs as the villain groups menace Paragon City and react to player victories and defeats.
http://www.cityofheroes.com/Screens/screen_85_thumb.jpg http://www.cityofheroes.com/Screens/screen_83_thumb.jpg http://www.cityofheroes.com/Screens/screen_82_thumb.jpg
http://www.cityofheroes.com/Screens/screen_80_thumb.jpg
You can acess trailers and more screenshots from HERE (http://www.cityofheroes.com/)

Like the screenshots! Looks very pretty.

Agreed.