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No "AoE" looting;
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Far fewer graveyards;
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Far fewer flight points;
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Mailing takes an hour when sending to alts or guildmates;
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No more shared gathering nodes (you take it, it disappears for everyone);
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Having to mine ore veins more than once to get all the ores/stones within;
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Having to stop leveling to go train new abilities and/or ability ranks;
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Your favorite race (draenei, goblin, blood elf, etc) is not available;
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Older graphics;
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Having to keep an eye on spell reagents (including warlock soul shards);
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Horde/Alliance/neutral auction houses no longer linked;
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No 'dual spec';
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Fixed raid sizes;
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Cannot create characters of opposite factions in PvP servers;
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Hunter pets need to be kept happy, i.e. feed them specific food often;
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No transmogrification;
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No mount/pet collection tab. Each occupies one item slot in your bags;
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No PvP arenas;
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Mounts can only be trained at 40 and 60, and much more expensive;
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Other - please specify in your post.