Ethereal Odyssey is a massive modpack with almost 200 mods. It has a lot of content, including 8 dimensions and almost 200 biomes to explore, 25 bosses and hundreds of new mobs to fight, many new armor and tool sets and a lot of quests to do.

Some of the features of this modpack are:

Modifyable weapons that can be crafted out of their individual parts at a tool forge
Upgradable wands that can be charged with mana to use powerful spells
Heart containers that can be obtained through quests and will permanently increase your health when used
A reforging system that lets you alter the stats of your gear with a reforging station
Wall jumps that let you climb up walls
A new difficulty system that will increase the health and strength of mobs over time
Waystones that can be found in villages or crafted which let you teleport between each other
Underground biomes
A new enchanting system called the Matrix Enchanting System
A disenchanting table that lets you move enchantments from various items onto books
Trumpet Skeletons

... and much more

You should at least reallocate 4 GB of your RAM to Minecraft while running this modpack (You can do so by going to the launch options of your profile and replacing the JVM argument "-Xmx[Current Number of Megabytes allocated to the ram]m" and replacing it with "-Xmx4096m" or something higher if your hardware allows you to do so.

If you want to make a server with this pack you should at least hava 8 GB of RAM available or it will lag quite a lot.

Note: This modpack is still under development, so when updating to a different version of the modpack, look at the changelog of the new version as some mods or items may be removed in future updates. If you want to keep items that have been removed you will need to change the config file of the mod that item is from and if you want to keep a removed mod just put it in the mod folder of the pack.