One time, a seasoned veteran player said to me, "You really have to play it to understand."

Dark Souls: Just a push more difficult than III. Somewhat linear. You may have some conundrum moments navigating around. Status effects are frightening however.

Dark Souls II: The "I have no idea where to go and this is rather BS hard AF."

Dark Souls III: Linear progression with optional extra exploration bits, You will not get lost. Easiest of the three. Recommended for beginners.

On another note, co-op is very fun. Throw a party! Or I mean, a gank. Sit back and wreak havoc.
Not feeling it? Try PvP.

And most importantly....