About Modded Minecraft
There are multiple genres of modpacks, most of them being the automation kind which is also what I prefer. Within automation there are more genres typically in the three categories kitchen sink, progression, and expert. Kitchen sink modpacks are generally just collections of mods where you can generally access what ever mods they want to play right from the start. Progression modpacks have changed recipes so that to gain access to certain mods you'll need certain materials from other mods. Expert modpacks are progression modpacks just with a large increase in resource demand and number of processing steps for items. This increase essentially necessitates that you have machines automating these steps in advance. I mainly play expert modpacks, however I wanna play more progression modpacks. "Completing" a modpack is subjective, however typically in progression modpacks there is some sort of questline that guides you through the custom progression in the modpack so generally completing all the quests counts as completion. Expert modpacks are the same way but typically have some sort of final item which just making on it's own is enough to consider the modpack complete.
My Past Experiences
I've been played Modded Minecraft for a LONG time now so I have a decent bit of experience in it. I haven't "finished" many modpacks however that's moreso lack of interest than anything but I'm hoping to "complete" more Modpacks now that I'm documenting my progress. The only two modpacks I have played to completion are Enigmatica 2 Expert Edition and Divine Journey 2.