Elex has the Piranha Bytes trademark inverted difficulty curve: very difficult at the beginning, but becomes rather easy once you find the OP guns that stunlock enemies. Even then, you can still get smashed in melee combat if you relent on self-discipline.
The RPG rules are fairly familiar to anybody who has played a Piranha Bytes game, where stats gate use of stronger weapons. If you don't meet the requirements, you simply can't use a weapon. I'm not sure if higher stats increase damage dealt by weapons.
The world is large and detailed with four distinct biomes. Exploration is worthwhile, and there are a few secret areas to find.
Graphically, Elex was not spectucular when it was first released and even less so now. However, it's colourful and easy on the eyes. Voice acting is serviceable. I don't recall it crashing much, if at all, so technically it's pretty good.
Whereas many games have a simplistic choice to be made near the end of the game that determines the ending, dialogue choices throughout a given playthrough of Elex are what determine the ending, by essentially shaping the personality of the main character.
I don't why I enjoyed Elex so much, but I suppose it has most of what I personally enjoy in a game. As such, I recommend Elex without reservation.