So Obama met with Castro, Trump with Kim Jung-Un

What did Castro give up, or agree to give up, or anything like that in return for dropping sanctions?

I just Trump is doing something with NK that Obama was crucified for doing with Cuba and Iran.

In many ways … yes.

not only are the 2 events different (ie; can’t really compare them except superficially), Obama 's Administration did everything in secret in regards to any agreements with Cuba. (in other words it was a done deal without input from congress).

Obama met with Fidel Castro?