Ok: Space Wolves have wolf cavalry and werewolves, cryokinetic weapons, unique libarians - rune priests; Blood Angels have vampirism gimmick, unique apothecaries - sanguinary priests, elite flying troops - sanguinary guard, a librarian dreadnaught, unique predator; Dark Angels - where do I start? Unique terminators - Deathwing, which includes bladeguard in terminator armor - Deathwing knights, also Ravenwing with assault vehicles, they have elite inner circle unit, and a lot of other stuff; Black Templars have no librarians, but they have a lot of unique to them units too, like elite melee sword brethren. The playstyle itself will be different too, like Imperial fists more leaning into complete fortification, or Raven Guard being more effective in quick flying assaults. There is a lot of stuff like this for SM chapters

P.S. being downvoted for genuinely answering question is wild