...and how was playing it different from playing a D&D character?
Again I have to go with Gamma World here. While the gaming community of northern New Hampshire was dominated with TSR products as best as I can recall, this was the only game I was immediately aware of which got me out of what was becoming a repetitive exercise of dungeon delves with no connected world to belong to.
So I ended up with my first non D&D character being a lithe lad with mental control, and distended jaws like a python from a run down village in my friend Randy's campaign world. A group of Gamma World characters are a wild card bunch of strange powers and disadvantages and for me made me try and think of effective ways to make the character and the group work effectively together. Again, at fifteen years old this was not too sophisticated a program. Mostly it was based on starting with more hit points at first level than any of my long surviving D&D characters ever achieved! Therefore getting into conflict and combat with the unknown was done with complete abandone without much thought to long term planning. But a blast on two liters of Mountain Dew anyways.