WoW is a very complex game that you learn one easy bit at a time. Max level is where all you have learned while leveling up comes to fruition in some very tough end game raiding and PvP
Too true. While it might seem mind numbingly easy in the beginning.. it starts to pick up and you get more and more skills to work with. They introduce them at a slow enough rate that you're comfortable with using them. By the end, you have a billion skills / macros / things on your bars and you know what they all do. If you've never played and look at a lvl 85's ui, it can be entirely overwhelming lol. They introduce things at a nice rate tho.
Also, side note for anyone who hasn't started playing cataclysm yet or doesn't know whether they want to get back in it: They've seriously improved so much. They've improved the system once again, making things less tedious. However, other things have been made more challenging (heroics are actually difficult now.. require cc / communication). I've bitched significantly in the past about BC and Wrath issues.. but so far, Cata has been great. Trimmed the fat, expanded on the good stuff, got rid of some of the bad. It's still a little too easy to get epics, but at least not for a little while (heroics don't drop epics anymore).