I'm new to ARPGs, and I've had fun with POE so far...

EDIT: Thanks so much for all the information guys! This has been HUGELY informative. I'm looking forward to progression now more than ever, and I'll be sure to share all of this with my similarly disenfranchised newbie friends.

but I'm nearing the middle of act IV, and I feel like I'm missing something. So many of the reviews on steam, and the people I know who play the game have like 3000+ hours logged, but I can't seem to figure out what they were doing all that time. With 25 hours logged (one character to act II, one to act IV) I haven't really felt challenged yet, and the only time I've died (or even really come close) was during the boss fight in Act III.

Most of the games I play there is an end goal on the horizon that you're working towards. In competitive games that end goal is overcoming other players, usually with a ranking system involved. In games like Summoners War the progression itself is the majority of the game, with huge benchmarks you have to work towards and overcome. Many MMOs blend these two, with the first chunk of the game being PvE that prepares you for PvP. In roguelikes/soulslike games the goal is usually to achieve mastery over increasingly difficult and complex systems.

Where does PoE fit in? Once I beat the story the first time, I can run it again right? Is the second run challenging, or is it more just an exercise in completion like the first run has been? What about after that? Is PvP a big deal? If so, is that something I can look forward to on my main character, or is it relegated to the PvP characters I've seen in the creation menu? I guess what I'm asking is, what content do I have to look forward to?