The if in this sentence is roughly equivalent to however, as in
It is compelling, however, it is at times depressing.
Note: Some people might feel that however is too strong; this I believe depends on one's personal idiolect.
The Cobuild Grammar (section 8.72) calls this construction a concessive clause.
In general, the if in that construction implies reservation, as for example:
Many libraries have little if any control over their patrons.
or introduces a contrast as in
she was honest, if a little brutal’
Other synonyms (which can be used instead of if in this context) are
- although
- albeit
- but
- even though
- even if
- despite being
- in spite of being
- yet
- whilst
(Source: Lexico Dictionary)
So the second clause is a limitation/restriction on the first one. Whatever is compelling, is also sometimes depressing, and that might want you to argue against it.