In its early days WoW was pretty damn good, for a themepark MMO. It was a lot easier and more solo oriented than EQ and most previous MMOs, but that was generally a good thing, as some of the stuff in EQ was retarded. But overall, it hit just the right balance between difficulty and ease of use. Leveling took a long time, dungeons were huge, non-linear in many cases, and hard, mobs were relatively hard, you had to use actual tactics in combat, there was a lot of social interaction, as you had to get to know people on the server, traveling around the huge world was fun (especially getting to dungeons in enemy territory), and there were cool quests and class quirks.
It was later on that the retardation gradually seeped in. Multiple talent trees, switchable on demand, cross-server dungeons and pvp queues, instantaneous world travel, flying mounts, phasing, small linear linear dungeons, and all the other crap. Anybody with half a brain could see how bad these features were a mile away, but of course Blizzard didn't care, because all that matters is increasing profit.
The difference between early WoW and later WoW is best seen by comparing Blackrock Depths and Hellfire Ramparts (first dungeon in Burning Crusade).
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