My first experience with Monster Hunter was with Freedom Unite on the PSP, playing a demo that only just left me confused on how in the world I'm supposed to play. It wasn't until I badly needed a new Wii U game in the first-year drought that I tried 3 Ultimate's demo, and it actually ended up clicking with me better. I was still a clueless beginner on several things, but I understood it enough to keep playing until I hit a wall and then rethink how to overcome it. I didn't even reach High Rank, yet I put a lot of hours into it.
Then 4 Ultimate released, and that's where I fully clicked with the series. That was my near-daily game to go through from the moment it came out up until my last few days of high school. I used to do a quest or two before my first class would finally start. My knowledge wasn't expert-level, but I got into G-Rank, so that accounted for something. I've been into the whole series since then, Stories series included.
All this started from there being no other Wii U games to play in the first few months of launch. Funny.