He got corrupted with the hate, it took over him. That's why when he could of decided to follow itachi's way he didn't and went down the path of evil and hatred and that was to kill the elders. After being more corrupted with hate he decided everyone should die.
Totally agree. The poor boy suffered true, but likes of Gaara, Nagato etc suffered too and gradually recovered from their trauma. If a madman does a murder can u set him free? No, u need to keep him in a asylum untill he is recovered instead of putting him to death. He has a right to kill the elders, but the normal konoha people Hizune, the academy teachers etc were the people who took care of Sasuke when his family was killed; So none save the elders and the root deserves to die. Personally, I dont want Sasuke to sink to the level of a common murderer, he still can be a hero.
As for Sasuke's power list:
1. Sharingan- Birtright.
2. Katon- Clan specialty.
3. Raiton- Taught by Kakashi.
4. CS - Given by orochimaru
5. MS- awaken by feeling the grief of loss
6. EMS- Taken from Itachi's corpse = Grave robbing/ stealing (Itachi didnt want Sasuke to have his eyes as he planed to put him in Ka if he found using Itachi's eyes)