I can't recommend the series enough. I will say the Prime games are still Metroidvanias first and foremost, and shooters a distant second, so they may still be worth your time; but also yeah, the 2D games are probably a good place to start. Zero Mission is both chronologically earliest and made to be an ideal entry point to the series. I'd still say to give Prime a shot after that to see if you vibe with it, then from there go on to either Prime 2, (my personal favorite!) or skip ahead in the timeline back to the 2D entries with AM2R or Samus Returns.
Either that, or try original NES Metroid and go in release order, if you have a tolerance for older game design and Nintento Hard difficulty. That way, you can get acquainted with the series through its mechanical evolution.
Just whatever you do, don't start with Super or Dread. Both of them are VERY good games, but I've noticed people who start there tend to have a harder time enjoying and appreciating the rest of the series, compared to coming into them from other entries.