I didn't know that Neon Genesis Evangelion had a manga adaption until I finished watching the original anime years ago. Initially, I hesitated to read the manga adaption because I thought it would be drastically different and I don't want my memories of the anime to be ruined. I looked up information about the manga one day and saw the manga author was part of the original anime crew. My fears subsided since that would mean the manga would not differ much from the anime.
It has a been a while since I watched the anime (haven't rewatched it on Netflix yet), so I can't pinpoint a lot of differences. The story is identical to anime, but there were subtle differences in how the plot progressed. One difference is Shinji Ikari. I like how he appeared in the manga because he had the right mix of sad and not sad moments (if that makes sense). Not to mention, I felt like I understand him better because I get to see more of his thoughts. There was little filler material in the manga compared to the anime, which is understandable since manga and anime are different mediums. I'm glad there wasn't a lot of filler in the manga because the pacing would be odd and it would've been boring if it was exactly like the anime. Also, what works in anime doesn't mean it would work out the same in manga and vice versa.
Since the mangaka was involved in anime production as a character designer, the characters and the scenery are just as beautiful as the animation. The Angel battle scenes are just fantastic to look at, but due to the manga being black and white, it becomes hard to tell the EVAs apart during those scenes. I sometimes have to re-read the dialogue to understand which EVA is which. But that is a minor thing for me, and it didn't detract the experience for me. I found it as an excuse to look at all the details in the pictures.
The five omnibus volumes I owned include bonus materials like interviews and commentary with the staff, which I recommend reading if you're interested in the production of the anime. There is also an index which translates the Japanese SFX that appears in the manga. It's fun to see how much onomatopoeias there are for many objects and actions in Japanese.
That is enough of my gushing of the manga, but whether you watched the series or not, check out this manga.