It was gorgeous. The city construction options were original takes (at the time) and presented a neat “tall vs wide” option to growth (if you got cut off expanding to new territories, you could build more districts in existing cities. Both counted the same towards the happiness cap). It took a stab at some neat asymmetry nearly up to the level of Endless Space 2. Did I mention it’s still the most gorgeous 4X ever made?
But it mostly fell apart in practice. The race balance was laughable (one race was all but invincible to being attacked). The quest-line victory broken. The tactical combat time-consuming without being deep. Zero penalty to declaring wars to the death with the advantage going to the attacker instead of the defender. And the biggie: the game was simply a race to who hit tier 2 tech first because the jump in equipment quality was huge and you just steamrolled the planet at that point (picture the swordsman upgrade rush in Civ 6, only much worse and without war weariness or any defender advantages).
A lot of the same systems are in both games. Map divided into territories that can each have one new city built, or annexed for an income bonus. Influence is a separate resource used for both diplomacy and spells. The same Master of Magic army organization.
I haven’t dipped into Planetfall much, but I can already tell the unit customization options are a lot deeper (I think EL was just simple gear stat upgrades). And the race balance couldn’t possibly be as bad as EL.