In patch 2.3, Blizzard is reducing the amount of experience required to level by 15% (for levels 20-60). Most people are happy about the change, though there are some people (such as Tobold) who questioning if this devalues the existing levelling game.
I would like to look at it from a sightly different angle. Let's define a concept called Time to Max Level. It's basically the amount of play time the average player would have to spend for her first character to reach the level cap.
Here's my question:
Should Time to Max Level depend on the value of the max level?
I think that it should not, that Time to Max Level should be independent of the numerical value of the max level. That there's a sweet spot, probably around 8 months, where someone who is new to the game and plays a couple of hours a week can eventually reach the cap. Reaching the cap is a major milestone, and should be in reach of every player. If that basic goal seems out of reach, it's very discouraging.
When WoW first came out, many reviews praised it for being easy for even casual players to hit the level cap. The actual number of the cap didn't matter, only that people could reach it.
But if it takes 8 months to reach 60, and 4 months to go from 60-70, that's 12 months to reach the max level. And when the next expansion comes out, that's another 4 months. Soon it will be impossible for a new player to reach the max level before the next expansion comes out.
Of course, if you add more levels, you need to make the levelling time faster for the earlier levels in order to keep Time to Max Level constant. So I think that Blizzard is on the right track with speeding up 20-60 levelling. I hope they continue this trend with the next expansion, speeding up 60-70, and trying to keep hitting the level cap within the reach of even the most casual players.