powerful doesn't mean solo

Diablo 2 and Borderlands have proven that it is not necessary to make classes difficult to solo to encourage grouping.

retutorials

It has become almost mandatory to include a tutorial process at the beginning of any game. That's great. But how often are you only partially through a game when something distracts from it for weeks or even months?

A tutorial at the beginning of a game's campaign isn't of much use then, because you don't want to start over. Explanatory videos are not much better than simply showing you a control map before dumping you into the action. A tutorial split into a series of active experiences can feel tedious, largely because after each one you're confronted with a list ("Four more to go..." /sigh).

Games with complex control schemes might benefit from what I'll call a "retutorial" — a comprehensive hands-on experience, similar to the introductions of many campaigns, which can be played at any time.

The main difference between an introduction and a retutorial should be a lack of emphasis on story, allowing the player to skip any assignment which covers something the player remembers. Give the player some control over the pace and content.

Most big games ramp both the complexity of controls and the difficulty of encounters as the story progresses. Players shouldn't feel like they're jumping onto a speeding train when picking up where they left off.