Technically LoS1 was an action-adventure game. There was plenty of exploration and puzzles in some levels. I remember several levels just consisting of platforming and puzzles with no fights. I too later completed the entire game on Paladin difficulty and I can certainly say that it was pretty challenging especially fighting Satan on Paladin. Took me 1 hour to beat him on that difficulty.
However with all upgrades brought and unlocked I found that Paladin difficulty later became easier especially with the light magic's whirlwind attack which not only damages enemies in a wide area range but also heals Gabriel at the same time. I've actually beat Satan several times on Paladin difficulty since the first try and it only takes a few minutes each time now.
What was amazing about LoS1 were the environments and how the music fitted so much. The game's story isn't just told through cut scenes and the narrator (Zobek) but also through the levels themselves. As you progress further into the game you feel as though you're getting further and further away from humanity and you even see this as you come to some rather dark fantastic places which IMO references Gabriel losing his humanity at the same time. So asides from the fluid combat, beautifully designed areas and great exploration and puzzles, LoS1 also had a great story going for it. For me the game was 2010's best action-adventure game.
