One of the reasons I always liked Orochimaru is because you never really saw his full power, he retreated or the fight was interrupted before he went all out. He's feared as one of the most dangerous and powerful shinobi in history, with perfect reason. Even Kakashi, who himself is renown and was powerful enough to become Hokage even after losing his Sharingan, was terrified of Orochimaru the first time he met him (in canon). When Orochimaru attacked Konoha, Ebisu said Jiraiya was the only one who could have possibly killed him. Sasuke himself admitted the only reason he was able to defeat Orochimaru was because he was weakened.
Let's just have a quick run-down of his abilities:
- All the basic nature transformations, along with Ying and Yang Release
- Wood Release/Healing Power due to his Zetsu body, which I'm also assuming he doesn't need to replace
- Very powerful chakra
- Was able to hold his own against Four-Tailed Naruto without his arms and with his current body failing
- Skilled in medical ninjutsu
- Can summon up to three Rashōmon
- ALL the snake jutsu, and his Zetsu body may allow him to use Senjutsu
- Skilled in kenjutsu
- Can literally shed his skin to regenerate
- Skilled in fūinjutsu, which he can even use in the middle of a battle
- Assimilated Kabuto's knowledge of the Impure World Reincarnation, using it to improve his own
- The blood of his true form is poisonous
- One of the most knowledgeable people in the entire series, he and Kabuto were able to partially decipher the Uchiha Stone Tablet and conclude that Tobi was not the real Madara
- Who knows HOW many revival plans he has in place
- Physically strong enough to knock down a full grown tree with a single kick
- Skilled in tracking, espionage, escapism and assassination from his time as a Root/Anbu member
By the end of the series, it's safe to say that everyone who isn't an Uchiha, Senju, Uzumaki or Ōtsutsuki is effectively irrelevant. However, I'd like to think that Orochimaru would still be up there as one of the most powerful shinobi. While I don't think he'd be a match for Rinnegan'd Sasuke or Six Paths Naruto, I think he could have given Madara (or maybe even Kaguya) a decent challenge.
So, given everything he's known to have accomplished and all the abilities he's known to have: at full power, how strong do you think Orochimaru truly is?