The First offers many RPG based elements to improve gameplay, including but not limited to improved combat, new weaponry, plenty of new mobs and bosses, and even dimensions! Not to mention the Origins mod which adds new abilities on start up to truly change your experience.
On the topic of gameplay experience, the farming and food system is completely overhauled in this pack, including TWO different food based mods, a timber mod, and easy harvesting.
The First also offers a huge expansion to building including 90+ new blocks, both Macaw and Mr. Crayfish furniture, Tinkers Construct, and easier bridging.
The dimensions added include but are not limited to the Twilight Forest and The Aether.