I like the series. My only problem with it is that the newer games are too guided. Metroid I, II, and super metroid (metroid 3) allowed you to explore more. Fusion and Other M was incredibly restrictive and guided.
My only problem with the Prime series is that you are in a first person point of view the whole time. The plot is good though.
Other M was a great game gameplay-wise. The writing for Samus was dreadful. The writers made her look weak. Look at how she was in Fusion. She had emotions and monolouged from time to time, but she wasn't so wishy-washy and didn't take shit from anyone. Plus, that whole thing with her freezing up in front of Ridley should have never happened. I can buy them trying to make her seem more human, but they really overcompensated in that respect.