Tā de shuǐpíng yě jiù chàbùlí, búsuàn tèbié tūchū.
His level is just so-so; nothing particularly outstanding.
Tips
usage
差不离 is the colloquial northern cousin of the more standard 差不多 (chàbuduō, 'about the same'). They overlap heavily, but 差不离 sounds more spoken/regional and can also mean 'mediocre, run-of-the-mill' - a nuance 差不多 doesn't carry as strongly.