In my opinion (Rest is my opinion, skip if you don't wanna read just post yours if you want); he was a little too passive:
This was his main flaw, he was to soft.
Hence why he let danzo do what needed to be done.
-Letting Danzo do to dirty work
He did let danzo run to free yes.
But danzo did his job, He may of been cruel but he kept the leaf safe for many years, No matter what stood in his way. Thats all a hokage can ask from a shinobi of the leaf.
Hence why Hiruzen never punished danzo for his action against the uchiha, Because deep down he know it had to be done sooner or later.
Again it had to be done. Danzo stated himself if things got to bad hiruzen himself would of acted. Danzo simply didn't want to risk it getting that far so he did what Hiruzen tried to delay.
For hiruzen, Someone who thought of the leaf as his family it was a tough choice, Thus why he tried to buy more time.
-Sacrificing Hyuuga Hizashi to avoid conflict with Cloud village(in summary in case you don't remember; a situation between both villages after conflict; Cloud ambassadors come to Leaf for peace treaty, but in the night they attempt to abduct Hinata. The Cloud ninja attempted abduction killed by Hiashi during the attempt. Leaf informed the situation to Cloud, but Cloud denied and claimed Leaf broke the peace treaty, therefore demanded Hiashi (clan leader's) dead body; but instead Leaf give Hizashi's (Hiashi's twin) body since Hizashi's branch family seal on his forehead that seals byakugan, therefore prevent giving the byakugan's power to enemy even after death)
Even though the cloud was in the wrong. it was either one Hyuga or war.
Whats worse? Losing one of your shinobi?, Or causing a avoidable war where many more shinobi would die in vain?.
-Letting Orochimaru go like that after what he did through village (murders and experiments)
Yes this was a
dick move, Most likely his worst mistake as hokage.
-Sasuke and Naruto...Why these kids suffered loneliness? Okay forget Sasuke atleast he was popular and liked among kids; but why he did not go to Naruto, talked to him, spent some time etc.? He was busy maybe because of his position, but Tsunade was able to give training to Sakura despite her position; he could atleast spend some time with the kid even for a little to make him believe that he is not on his own.
I'm sure a hokage has more things to do than look over two children. There are children in every village who suffered loneliness.
Gaara had a bad time as a Jin, I'm sure Bee did also. It wasn't simply isolated to the leaf.
The kages of the villages can't really be held responsible for the way their villages feel towards each other