The Ark has many features to offer. In SP, there are 5 types of game-play. 1.) Survival & Taming. 2.) Homestead/base-building/ Crafting 3.) Exploration 4.) Battle/Conquering the story. 5.) Creative. Dinos are the NPCs. Basically,
Survival &Taming - Its like Minecraft in survival mode, but with more aggressiveness from the creatures and not as blocky/cartoony/kiddie. Not only just creatures, but even the elements are out to kill your character. Snow, Cold, Heat etc. Taming is important because tamed Dinos act as pack-mules/guard dogs/horses (300+ when counting the variants). Some are simple to tame, some are not tame-able. A few are not agressive, Some will flee, most will attack you, Some will hunt you.
Homestead/Base building/Crafting - Heavily involves gathering resources (which there are many different resources ).You even craft your character...(skin, body style/build, Hair and eyes, etc. You Start the game with only your "Undies"for clothing. Tighty-whities for men, basic Bra and panties for women. You want real clothing, make it! Materials go from Stone-age to Space-age..."Minecraft with better graphics" ( Note; There is Pixel-ARK for those minecraft lovers now too, ARK in the minecraft blocky/cartoony/kiddie style)
Exploration - There are many clues that make up the SP story that you have to locate. Also there are Arena/end bosses that you have to hunt down key artifacts to unlock the different Boss arenas. The artifacts are found all over the map. On land, on cliffs, in volcanoes, in swamps, in caves, at the bottom of the ocean, and even in ocean caves where you can die very quickly because your lost/trapped with no air.
Battle/Conquering the Story - You will need an Army of tamed Dinos to take on the arena bosses. Your reward for taking on the storyline, is Ascension.
Creative - Forget the story and just build....like minecraft! (Note: there is a "Structure Limit" of 6000-7500 items placed "Within the area of render", more so on consoles...i.e. Limited Hardware issue.
AND the game is MOD-able, the company even encourages, promotes, and sometimes sponsor mods.
as for SP vs MP, its really personal taste...
I play SP mode because over the last few years, MP only seems to attract Trolls/hacks/ID-10-Ts that dont play by rules, that cheat, lie, and steal... in my opinion.