Hewwo! I thought I would talk about my ingame experience!
To start alt experience means alt character experience. As I have stated many many times, Rhel'a is a cherished alt of mine ^w^

My expansion checklists go like the following:
  • level up DoM/DoW to the expansion level
  • level up DoL/DoH to the expansion level
  • gear up (everything)
  • complete job quests (everything)
  • max of tribes
  • unlock every trial, dungeon, raid, and alliance raid (barring extreme/savage/ultimate)
  • unlock specific side content (exploration, things like doman restoration, etc)
  • complete deep dungeon story floors
  • log every fisher hole and common fish
  • complete every yellow quest
  • max out mount speed and unlock flight for every region

and so on...

If you want to see what the stormblood list looks like here is a copy paste of it:
ffxiv stormblood checklist:

mount travel
  • get flight in every region I missed
  • max out mount speed for every SB region

DoM/DoW/DoL/DoH job leveling etc
  • DoM/DoW jobs leveled to 70
  • gear up DoM/DoW jobs
  • DoM/DoW job quests completed
  • level up crafters to 70
  • level up gatherers to 70
  • gear up crafters
  • gear up gatherers
  • complete gatherer and crafter quests
  • obtain every Level 70 Tomes of Regional Folklore
  • obtain every Level 70 master crafting books
  • unlock wondrous tales

Overworld side content
  • unlock every SB tribe
  • Complete SB Hildi questline
  • complete SB tribal alliance quests
  • complete every HW yellow quest
  • complete every SB yellow quest
  • complete SB sight seeing
  • unlock SB exploration (Eureka)
  • log fisher locations
  • log every common fish

dungeons, raids, deep dungeons, alliance raids, trails, etc
  • unlock SB alliance raids and complete questline
  • complete HoH story floors

post stormblood
  • try Doman restoration at least once
  • unlock every extra dungeon and trial SB has to offer (barring extreme/savage/ultimate)
  • get blue spells (97, 98, 101, 102, 103, 104)
  • unlock SB custom deliveries

Add to endwalker list
  • log spearfishing locations
  • catch every monster fish (and red collectable)

well, I am in stormblood now. I have done a lot of things I have never thought to try and enjoyed the game deeply. Today I finished up the fishing for HW zones that I forgot to do last expansion and finally got myself a magic bucket. I'm so proud of it! I also got some baits ready so I will be ready to complete the fishing logs (only common fish) for all the sb zones. I got a majority of my stormblood list completed and now it is only a matter of time.

To contrast I will talk about my main character, Ailbhe. On that character, I mainly played the main story and not much else. I did try side content but for whatever reason thought to continue onwards with main story content only.
By comparison, the enjoyment is different between the two characters. Though, I am having more to look forward on this alt. I do wonder what I'll think when I hop back on my main. Likely will be reconfiguring a lot of HUD things and make a few helpful macros for myself!

Has anyone else embarked in a long journey of side content? If so, what is your experiences?