Firaxis et al
On behalf of gamers everywhere; all you have to do to make this game AMAZING is a graphical update and some small gameplay (AI for instance) tweaks. Take the example of other older games with amazing gameplay that developers wanted to "improve" upon. The games were mediocre at best and the "improvments" were the cause.
The original XCOM can be run on most phones nowadays with processing power to spare, but people still play it. Not for the bells and whistles and certainly not for the massive pizza sized pixels, it's the gameplay. This is pretty much the Holy Grail of classic computer games. Don't screw it up.