French city on river is comparatively pleasant (5)
I believe the answer is:
nicer
'comparatively pleasant' is the definition.
('nice' is associated in meaning with 'pleasant')
'french city on river' is the wordplay.
'french city' becomes 'nice' (Nice is a French city).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'river' becomes 'r' (abbreviation).
'nice'+'r'='NICER'
'is' is the link.
(Other definitions for nicer that I've seen before include "it's more appealing" , "Even more 7 down!" , "more lovely" , "better" , "More pleasing" .)