Rather than simply be: "Diablo 3-From the beginning", I feel that seasons would benefit from being treated as community events in addition to being treated as competitions.

For example:
A season near winter could focus on ice-based skills, items and enemies. The exclusive legendaries would offer up bonuses to cold skills, Elites and Champion packs would be more likely to spawn with Frozen or Frozen Pulse, and there could be a challenge asking the community to slay X amount of enemies with cold skills before the end of the season, netting a reward to all season players if met and perhaps even offering up a unique Conquest and Banner Sigil for the first 1000 to kill 5000 enemies with cold skills themselves.

This would keep seasons from getting too stale, it could provide players with the push necessary to try out new builds and ways to play outside of their comfort zones, and could serve to bring the community together.