That i remember, but how skillful is he?
By default he's at least on Hebi Sasuke's level because Orochimaru was the one who taught him everything about Kenjutsu. Orochimaru has many more years of experience with swords, is known for his proficiency with Kusanagi.
Kusanagi is his choice very often when it comes to fights - against Hiruzen, Kyuubiruto, Itachi, Sai.
Oro's sword is way stronger than Sasuke's sword which is a mere replica of original Kusanagi. Orochimaru is proficient in fighting with Kusanagi, throwing (spitting) it with deadly precision and using it remotely (his telepathic Kusanagi fighting skills were praised in 2nd Databook).