Not so wonderful as to stop you in your tracks? (8)
I believe the answer is:
passable
'wonderful as to stop you in your tracks?' is the definition.
I can't judge whether this defines the answer.
'not so' is the wordplay.
I cannot quite understand how this works, but
'so' could be 'as' (eg 'not as tall as me' means 'not so tall as me') and 'as' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for passable that I've seen before include "Good enough to be acceptable" , "Fairly good but not outstanding" , "okay?" , "OK" , "Barely adequate" .)