>>713939093 (OP)Prime 1 is good, but it's a proof of concept.
Lots of small stuff that isn't polished/doesn't feel great compared to the later games, like the platforming, the way the morph ball handles, the amount of empty hallways between each area, the end game enemies being different colored versions of Metroids and Space Pirates which are only weak to the corresponding beam type, the way Magmoor is connected to everything and Phendrana is only accessible through Magmoor, and a few other small issues.
Prime 3 is like the complete opposite of this. The controls are completely polished, the way Samus handles in the morph ball and the way jumps and platforming works feels better, most of the areas in the game are way better laid out with rooms having compact designs with more interesting stuff in them and less pointless hallways, combat stays interesting through the whole game (ignoring the flaw with Hypermode trivializing the game), and so on...
If Prime 1 is a proof of concept, 3 is definitely the most polished version of the same idae, with improved art on top of it all...
...except it's completely casualized. Game is quite easy once you figure out the trick with hypermode, and even ignoring that, the puzzles are extremely easy, items are kind of just handed to you by being laid directly in your path, and so on.
Prime 2 is almost all the polish of 3, but with a difficulty that's higher than 1.
The light/dark + insects + horror themes of the game art-wise aren't for everyone, but it's also arguably the best art in the series with the most cohesive visual theme (since the whole planet is devoted to the Luminoth) and arguably gets the closest out of the prime games to feeling like the original Metroid 1, 2, and Super with the horror/cave exploration alien atmosphere.