I never read him as an Atheist. I do realize he was basically kicked out of the Jewish community though and am aware of the problems he had and how controversial he was at the time. Ill have to go back and read more carefully another time and take note of the deterministic attitude vs finite mode although either way I dont think itd be inaccurate to describe his philosophy as pantheistic, particularly to the layman who isnt big into philosophy. Philosophy heads may dispute the nuances a bit more..but even many of those would at least say his conception of God/Nature has many common characteristics to pantheism.
I'm pretty sure we're essentially saying the same thing, just with slightly different definitions, so I don't want to give the impression that I'm totally disagreeing with you, there are tons of books by guys smarter than me backing up your claim.
I think that it's more useful to describe him as an atheist, since his God isn't transcendent at all. Plenty of atheists have justified true belief in logic preserving truth value and gravity exerting a force on massive objects, and these are overarching truths that don't necessarily conflict with their self-identification as atheists. Spinoza's God seems (to me) to be a carefully worded version of these conceptions.
But, yeah, I'm just a guy on the internet that's done a little bit of reading, not a philosopher. I would recommend Steven Nadler's book on Spinoza if anyone's interested in working through the Ethics.