If you have seen it, can everybody who has just agree how much more sense it makes? The 2003 series’ Wrath is CONVOLUTED AS HELL (SPOILERS Oh, look! It’s a kid who was a failed human transmutation who is actually successful and was sacrificed to the Gate of Truth in a ritual that required sacrifice to make him in the first place and turned him into a weird black baby who took Edward Elric’s limbs to live in our world in an island for years until the Elrics’ found him, and yadayadada END SPOILERS), and the twists at the end are just too much for my brain to process (Parallel worlds? Nazis? Couldn’t Ed just kill himself to return back to Amestris? This doesn’t count as spoilers because knowing the twist before is better than going in blind).
I would recommend reading the original comic of FMA. If you have to watch it, then watch FMA: Brotherhood. The 2003 series surpassed the comic and just wrote it’s own story (which is why Brotherhood was made, in a way).
I disagree. The reason the 2003 series HAS to be seen first is because a. It’s good and cannot be enjoyed well after watching the fast-paced Brotherhood and b. It does total justice to Maes Hughes, who is EXTREMELY important to the main characters and their stories (especially Roy Mustang since an event involving Maes Hughes was practically the inciting incident for him to move on to Edward Elric’s level as a protagonist). If the 2003 series was created with the stories of the Homunculi and Dante in mind since the beginning, it might’ve made more sense.
Maybe you don’t want to watch the entire series, but at least watch the first 25 episodes, and that way you have around 10 episodes of recap in Brotherhood with a fast pace and as much new material as possible working from the manga/comic (counting Episode 1 and 11 as one because they do have 2003 series elements despite seemingly being their own thing).