Modpack with a focus on exploration and progression.

Mostly avoiding mods that you have to look up a wiki for.

Upgrading/Leveling your character:

Project MMO - Level up in mining, combat, etc. by doing those activities to get bonuses for those activities. Equipment is level gated.
PlayerEx - Gain Stat points as you gain Minecraft exp.
Everlasting Abilities - Spend Minecraft exp to gain permanent potion effects you find.
Lost Trinkets - Occasionally unlock passives that you can equip.
Spice of Life: Carrot Edition - Gain more max health by eating new foods.
Vampirism - Become a vampire or vampire hunter and and collect materials to rank up and gain more double-sided buffs.

Gear Progression:

Tinkers Construct - Smelt materials into weapon, tool, armor, parts and combine them to create equipment. Most materials have unique passives.
Silent Gear - Similar to tinkers. Less time to get started, less potential.
RelicEx - Items for your curio slots that give PlayerEx stats.
Apotheosis - Some items will have rarity and additional affixes that can be transferred to other items.

Plenty to explore:

Magic Systems:

The best storage system: Simple Storage Network

The best gravestone mod: Corail Tombstone

Mostly No Science (Forge)