Here's my take on the classes grouped by tier of awesome:
Gems: Avenger, Bard, Fighter
Each of these classes are well designed in terms of themes and mechanics. They are fun to play, though each in a different way. Fighters control the battlefield. Avengers dominate a target of choice. Bards make the rest of your allies fight better, while still doing his share of damage.
Exceptional: Rogue, Sorcerer, Swordmage, Warlord
Let's hear it for teamwork. Most of these characters play very well with others. They also throw up some great numbers when it comes to dealing or preventing damage. The Sorcerer is the one who plays least well with others, but he also had the most impressive damage-dealing functionality.
Decent: Barbarian, Cleric, Druid, Invoker, Ranger
All these characters are fun and have redeeming qualities, but are lacking somewhere or other. The Ranger and Barbarian aren't the best team players. The Cleric is more limited in his role than either the Bard or the Warlord. The Invoker's theme feels like someone put a new skin on a traditional Wizard while the Druid eats up extra time and power slots with his silly shape-changing routines.
Trash: Paladin, Shaman, Warden, Warlock, Wizard
The Wizard under performs until he reaches Paragon Tier, at which point he gets tricks that become so powerful as to become a buzz-kill. The Shaman is a dedicated "pet class," which 4th Edition was better for leaving behind. The Warden has ill-conceived themes. The Paladin and Warlock are largely broken classes with terrible core mechanics (Divine Challenge + Warlock Curse).
- Marty Lund