Sets released: Planar Chaos, Future Sight, Tenth Edition, Lorwyn

Major stuff:

   - Future Sight introduced the idea of players being more like objects
   in the game.  For example, protection was extended so that it could
   be gained by a player.

   - Future Sight introduced new card types ostensibly from the future:
     - The Planeswalker type was referred to but not used.
     - The Tribal type was used - it attaches a creature type to a
     non-creature card.

   - Future Sight introduced new keyword abilities for existing
   functionality:
     - The ability reach was introduced to represent the ability of
     a creature without flying to block a creature with flying.
     - The ability deathtouch was introduced to represent the ability
     of a creature to destroy creatures that it damages non-lethally.
     - The ability shroud was introduced for permanents or players
     that can't be the target of spells or abilities.
     - The ability lifelink was introduced to cover some of the cases
     where a creature's combat damage triggers life gain.

   - Lorwyn introduced the Tribal type "properly", using it on a number
   of cards to improve the flow of the "creature type matters" theme.

   - Lorwyn introduced the changeling ability, which grants all creature
   types.

   - Lorwyn introduced actual Planeswalker cards.  These cards have
   abilities that you can play one of, once, during your main phase.
   The card has a loyalty score and comes into play with that
   many loyalty counters, and its abilities cost an increase or
   decrease of a certain number of counters.  The Planeswalker may
   be damaged by effects that would deal non-combat damage to you
   (as a redirection chosen by the effect's controller) and may be
   attacked (you assign blockers for the Planeswalker as normal).

Minor stuff:

   - Planar Chaos introduced a "parallel universe" card frame.

   - Future Sight introduced a "future worlds" card frame.

   - Future Sight created a lot of combinations of ideas that had not
   been tried before, and may never be tried again, such as a land,
   an enchantment and an artifact with morph, and more general
   typecycling abilities such as slivercycling.

   - Some terms appeared on only a few cards in Future Sight: delve,
   gravestorm, aura swap, grandeur, transfigure, fateseal, frenzy,

   - Abilities champion, hideaway and evoke appeared in Lorwyn.

   - The Kithkin and Treefolk creature types were used more in Lorwyn
   block than ever before.