Most of the alleged problems of the original game could be solved in a very trivial way:
a) inventory management is tedious? - Make the game remember the equipment layouts for all surviving toons, add hints for weapons aptitude (a la "Warning: this soldier has low strength to carry Blaster Launcher, he'll collapse senseless after X turns of running' / 'This soldier has high psy score, equip psi-amp? etc), add "save/load profile" functionality to switch between sets of gears. After all, some x-com ports already have some of this (check SMK's pocket UFO)
b) TU math is hard? Add grid highlighting (like in HoMM 3), create a comprehensive tutorial that will show what a reaction shot is, why it's important to understand that you don't have 360 degrees overview and so on.
c) Game is too slow? There's a slider for movement speed and aliens' turn speed, use it Luke! "Last alien hunt" problem can be solved by programming alien to either suicide (with 0 turn grenade in hand) or to give up to the X-com crew (if you want it the gamey way), or by adding 'autoresolve' button HoMM-style.
d) Psi is unbalanced? Decrease chance of possession, increase TU cost (already fixed in some ports), add something like "Perils of the Warp" (tm) (reversed possession and so on).
And this list can continue on and on. The fact is, Firaxis, instead of improving on UI's usability and providing general QoL improvement like the ones i listed, decided to go the easy way.