Like Flapps said, we achieved the CRT-like effect using post processing effects. The game is fully 2D, but we used 3 main filters: vignette, lens distortion, and noise to add some grain.
There are ways to go further like pixel size and scanlines, but we've used those effects before and didn't want to ruin its style by applying it anywhere we can.
Thanks for your feedback on the shield as well. Most of our final playtesting involved tightening up player input vs. shield positioning, but there is still work to be done.