I started with a blessing and found the early game to be totally crap; because the cooldowns for skills are too long... I leveled pretty slow and people didn't seem excited to help me. I even had to farm my own Go To Hell !!!!!!!!, Panic, and Rahab's Spirit to make my Pride Soul. When I started getting to the point where it was in theory possible to help others with "healing", I found out that I could only get 1 unreliable heal off per boss fight. The guy I tried helping said to heal him, but I healed him not each time we went to Story Azrael and we died before the cooldown could reset each time, even if I healed him as soon as my heal could have the full effect on his HP bar (by %).
The 150k~>500k stat grind wasn't so bad because a Death got me Belial kills afk in a game that lasted something like 13 hours... (he came back to check whether he died; T3)
The late game of 500k~3M stats was pretty easy and rewarding as a Blessing T4. The Fallen Angel made farming stats a blessing!
Lastly, the end game of farming 1M gold and lumber was a pain. It took quite a while.
Of course blessing was not the only character I have but I felt it was important to give my "first" experience.
The second hero I made was Sephiroth. The third hero I made was Sitael, and the last one I made was Cloud.
At this point, I made a 500k lumber wisp with the help of a friend so I didn't need to ask others for the lumber grind assistance every time I wanted to make a new hero...
My Sephiroth is capped.
The cheaty-face hero Sephiroth allowed me to ignore many level limitations such as:
a) Jumping from Enuk to Bereth
b) Jumping from Gremory area to Ergot area
I can say though, that the grind from 500k stats to 1M strength was rough.
After reaching 1M strength, gaining stats smoothed out nicely thanks to Dark Barrier.
My Sitael is around 2.3M stats. (It lacks "Baal flag")
I can honestly say this hero was a bit of a nightmare in the beginning. Sure I had 500k stats from my Wisp, but the int had a questionable effect on combat. I took my Sitael to the agility route for items. After reach 1M int, I started gaining agility as the secondary stat, and found that I started killing significantly faster as my agility rose. I can smoothly afk at Belial without dying now, though the anti-afk still kills me!
(note: Keep in mind that the active skills are Int-based if you plan on taking what I said to heart.)
My Cloud is around 1M stats. (It is in Molloch, Molloch, Molloch, Lust, Pentagram, "Blaze Flag")
I've been unlucky for getting items to drop and gaining stats feels really slow. I've not played on him much but it feels really slow for gaining stats compared to my other heroes.
All in all, I'd say
Level 1 ~ 150k stats was enjoyable, but the skill cooldowns sucked...
150k stats ~ 250k stats isn't so bad
250k ~ 500k stats is a harsh reality (that my wisp allows me to avoid now!)
Beyond 500k, it really depends on the hero...
So in short, I don't know if early game or late game is enjoyable, but the section of 500k stats ~ 1.3M stats was probably fun. I got to play with other people the most then and kill bosses together. I got to "roll dice" and have fun with that too.