Personal Recommendations 

Massively Multiplayer

Ultima Online – One of the original and still the best sandbox titles on the market. Link is to the Unofficial Renaissance server since the official servers have essentially turned into a poor Diablo knock off. Free to Play

Ragnarok Online – The classic open world grinder with incredible character customization options and the original hat collecting game. Free to Play

Final Fantasy XIV – The best of the modern theme-park style MMOs. Has all the questing, dungeons, raiding you’d expect and a nice class system. License and subscription required.

AionTheme park MMO, has all the typical thing’s you’d expect but with a nice skill chaining system. Seems to be the best of  Free to Play options.

Blade and Soul Theme Park MMO with an East Asian theme. Excellent graphics with fast paced combat. Free to Play.

Hack and Slash/Action RPG/Lootfest

Path of Exile –  This is THE hack and slash game of the now. Incredible skill and character system. Heaps of existing content and regular content updates. Best of all it’s Free to Play

Grim Dawn – Single player focused (multi-player still available) game. It’s a slow burner, don’t expect to be able to rush and finish this in one sitting without risking death from sleep deprivation. This game has an interesting dual class system and “devotion” system to further customize your characters. Features faction system with some interesting quirks to it such as enemy factions hating you so much that their areas will spawn stronger monsters to kill you. Buy

Diablo II – The timeless classic, great class, skill, item system and atmosphere. You can generally find the game and it’s expansion bundled together fairly cheaply from various online retailers or key-sellers. Buy

Survival Sandbox

Don’t Starve –  Great art style, randomly generated maps and the environment can get unforgiving fairly quickly, if you’re finding other games too easy. Buy

Conan Exiles – Currently in early access. Survival isn’t too difficult however the joy comes from either competition with the players, building or exploration and in the future NPC threats. Competition comes from claiming and controlling lucrative resources and slaves (You can enslave NPCs to serve you or your clan in various aspects from combat to crafting). Building system is a little resource intensive at the moment but has the pieces for you to create almost any kind of building you want. Exploration is great as this map is hand-crafted with points of interest all over the map and dungeons for you to explore. Buy