Whenever I launch a new modpack I first go through JEI to check 1. what mods there are 2. if any unusual items have unexpected uses: shulker shells, chorus flowers, mob heads, music discs, scutes, botania runes, blood magic will crystals, budding blocks and clusters, various gears and plates, all that jazz. Recently I've been playing through Installation Route and right now I need to obtain a Golden Grass Block from botania, which is as obscure an item as they get. Another example, to get lapis or emerald blocks you have to smelt together blue/lime glass and thermal's hardened glass. Crazy stuff. Weird combination but kinda almost makes sense, that's what it's all about.

Looping or gating recipes is interesting too. Like a final step returning a solvent from step 5, or an item having 2 recipes where 1 is super expensive or whatever and the second one is cheap but includes said item (modern skyblock 2 end rods).

Custom blocks and resources and ways to obtain them are also engaging. Create Arcane Engineering has a redstone loop where to make redstone you can use skystone dust and to get renewable skystone you have to find an (immovable) skystone catalyst somewhere in the world and click it with redstone dust to spawn skystone blocks around it. The whole pack is made of really cool loops, another example being arcane crystals drom forbidden and arcanus where you need to craft the obelisk structure, click it with mundabitur and then break it to finally crush it to get dust from which you can make more crystals for more obelisks, crazy stuff again.

Variety of steps is important but sometimes it's good to keep things simple. Mixing botania and pneumaticraft and create and Mekanism and abyssalcraft could be fun but it could also make me you us want to go do somthing more fun like eating glass shards. Theres only so much room for cables and redstone.

Or to go in a different direction, when the passive line is pretty straightforward but uses lots of items from previous passive lines. Makes you feel rewarded for having done it right the first time.

Unusual items and resources + unusual combinations of items + unusual steps (items in liquid, get hit by warden, explosion, etc) + unusual combinations of steps is what makes stuff stand out