I wasn't aware that Venom *had* a plotline, beyond Brock and the symbiote both hate Parker. That's it, isn't it? We did lose the symbiote's pain of rejection, I guess.
Frankly, Venom was 2-dimensional in the comics and cool to look at. In the movie, he was one-dimensional and cool to look at.
Phoenix was interesting and complicated in the comics. In the movie, she kills Scott - why? She does nothing between killing X and Magneto's fall - why? Venom, while weakly done, at least made sense on the surface of it. Phoenix was nonsense in the movie.
Phoenix started off better in the original, and ended up worse. She was more mishandled.