I initially started off pretty strong, but interest dropped off to the point of only really playing an hour a day (if at all). I'll hit P26 tonight and probably put more time in once the next patch lands this week.
To be honest I'm not really in any kinda rush to level and would just rather enjoy the game more in general.
This all considered I think the time and effort needed to hit 100 is ok assuming you have access to gear / gem in hat to boost XP gains and will play at a high enough ML to make leveling less of a chore come next patch.
People who are playing now will play on a minimum of Monster Power 3 for +30% XP. They'll also equip a hellfire ring for +35%xp. If you have 5NV stacks at the moment with a ruby you have +~90% XP, which will now be +155%XP, meaning you level 58% faster than you normally do now, not to mention that there will be better gear dropping in higher quantities (with the ilvl63 affixes) meaning you can kill enemies faster and maybe move up to a higher monster power.
I still think it's a bit slow. I've played 2 characters up to around PL 11-12, and it's scary knowing that I've only done what, 3% of it?
The experience required is more than fine, and probably slightly too easy after patch, but i guess as a modern game it needs to be made easier so whining casual players keep playing. And the whole alt thing is just an excuse. "OMG I CANT PLAY MY ALT COZ MY MAIN IS PARAGON LEVEL 30 AND I MISS ALL THE GAINS". Well boohoo and slap on 90MF on your character and all you lose is bit gold in drops.
Getting gear equivalent to your current gear with 90MF on it isn't that cheap or easy