Seems like 2 ways we could read this?

Obviously one of the last direct formative influences from the golden age of adventure strips to turn up in mainstream comics - you can see it’s 100% Caniff & co. vibes without any secondary influence (say, Toth) as an intermediary 

His splash compositions have that Kirby widescreen chaos but seem to lack that clear narrative flow that Kirby could magically do - not sure where Robbins is trying to lead my eye, so it becomes a bit noisy

I dig his anatomy and action approach quite a bit, particularly with a sympathetic inker like Frank Springer

I admire the simpler, more cartoony faces in the middle of all that

Don’t know that I would have been a fan as a kid, but as an adult I can appreciate the skill and style.

Frank Robbins is one of the most lauded American cartoonists ever; Alex Toth, Milton Caniff, Jack Kirby, Joe Kubert etc all lined up to praise him. I despair when I see people dismissing his work just because he didn't look like Sal Buscema. It's just embarrassing.

Not regularly, but he drew a few of his later Batman stories (Detective #416,420-421,426,429).  #416 and 429 had Man-Bat if you want a taste of what might have been.  He also wrote and drew the Jason Bard story in Detective #435.

To the original question, his art definitely an acquired taste for me, but now I'm quite fond of his stuff, especially Invaders and the Shadow.

I think he was entirely an artist at Marvel, not "mostly."  I don't recall him ever writing anything for them.  The differing assignments he received at the two companies appear to stem from differing needs.  When Robbins broke in at DC in 1968, the company needed writers since they'd just fired a bunch of them in retaliation for their abortive attempt to unionize and/or get benefits.  Whereas when he switched to Marvel in 1974, they were expanding and were really in need of artists who could produce quality work on schedule, but they had an abundance of young new writers. 

To my knowledge Robbins never regularly wrote and drew any ongoing comic series.  I'm pretty sure the only things he both wrote and drew (in a comic book) were a handful of Batman stories circa 1973-74.

I think Robbins is definitely under-appreciated as a writer.  People tend to give all the credit to Denny O'Neil (and Neal Adams) for revitalizing Batman, but Robbins was right there too, writing half the Batman stories during that time period.  Robbins' Batman work was just as good as O'Neil's.  During Robbins' tenure there was a remarkable period of about three years in which not a single one of Batman's classic rogues' gallery appeared in Batman or Detective.  That has never happened before or since.  Not relying on costumed villains meant the writers turned to hardboiled detective stories or gothic horror, and the result was pretty great and did a lot to erase the memories of the TV series.  Among other things, Robbins co-created Man-Bat with Adams during this time.

You're not alone, apparently.  According to Roy Thomas, sales on Invaders went down after Colletta left.  Correlation doesn't necessarily prove causation, but Colletta definitely tamed a lot of Robbins' idiosyncracies and that probably made the art more accessible to 70s Marvel readers who were used to a certain look.  I myself liked Robbins' style enough that I didn't mind the switch to Frank Springer who was more faithful to the pencils.

I agree about the Johnny Hazard stuff; that was great.