OL have a lot of rules not sense...
why heroes can attack 2 time and monster no?
Play with a house rule that says monsters can attack twice per turn and find out. I've heard of several groups who missed that rule and allowed monsters to attack twice, the result is so far unanimously that the OL becomes unstoppable.
why heroes can revive each time, and OL have 1 monster with reinforcement?
Again, play with house rules to allow greater reinforcements and see how it works out for you. Maybe you'll discover there's a good reason they wrote it the way they did.
Why nerf card of OL when this card can be used 1 time, and instead a talent like Necromancer's "Fury of Death" can be used in easy mode with only 2 fatique?
Fury of Undeath requires an action AND to exhaust the card, in addition to the 1 fatigue cost. This means it can only be used once per turn and it soaks one of the hero's two actions in the process.
As for nerfing OL cards, I mostly prefer to play cards as written unless there's an obvious problem. If you don't like the errata, don't use them.
In order to be successful, the Overlord must be ruthless. He must play to win at every opportunity and he must not be afraid of making cheesy moves. It can be hard sometimes, being one against many heroes. The inclination is to put up a fight, but not so much that it starts to annoy the other players. If you want to win, you have to shake that.
It also helps to learn how to play the players. If the warrior loves to chase goblins and kill them, have your goblins run off to odd corners of the map to draw the hero out of position. Things like that. If the hero players have habits in this game, try to find ways to exploit those habits to slow them down.
Another thing that would probably help is to rotate who plays the OL. If you don't like it, it gives you some relief and lets you win as a hero sometimes. More importantly, it gives everyone a better perspective on the game. Maybe one of your friends will do something as OL that will make you realize the potential you've been missing.
Descent has a bad reputation of appearing unbalanced one way or the other to new player groups. I've heard plenty of people saying the OL is too weak, but I've heard just as many saying he's OP. The only thing I can say to that is, having played 1E for many years and 2E since release, I find the win ratio to be relatively even. It takes more than a few plays, though, to get into the swing.