Exceptionally good curiosities left (10)

I believe the answer is:

phenomenal

'exceptionally good' is the definition.
(I've seen this before)

'curiosities left' is the wordplay.
'curiosities' becomes 'phenomena' (curious happenings).
'left' becomes 'L' (common abbreviation).
'phenomena'+'l'='PHENOMENAL'

(Other definitions for phenomenal that I've seen before include "Extraordinary - help one man (anag)" , "Stunning" , "Mind-blowing" , "Amazing" , "Remarkable" .)

I've seen this clue in The Telegraph.

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