Once you realized "Hey, we're totally outgunned...we just need to flood the aliens until we get better gear", things changed. Missions became more about resource management: what is the bare minimum I can field to wipe these guys, what can I build and manufacture that has the highest profit margin, etc.?
Terror missions, for example, early on devolved into "Set fire to everything, because we need the light, and shoot the civilians, because they could be used to feed the Chrysalids and make more Chrysalids."
The enemies in the game stayed largely the same difficulty, but your equipment got better and better and tactics switched as you were able to field more expensive units--and unless you ran a really tight resource game, you treated those expensive units much differently.
The thing that made the game feel unique was exactly that: the reverse-difficulty. If you started kicking ass, and then things got harder, it'd be annoying--instead, you had some early success, discovered just how outclassed you were, and after a few restarts learned how to fight a technologically-superior enemy until you had achieved force parity.
At the easy difficulty modes (most new players) the curve is completely backwards. It stars out brutally difficult and becomes easier as you gain access to heavy plasma weapons.
If a total wipe of your early team was a forgiving event compared to late-game losses, that could be excused as setting tone, but it's not like that - players just save-scummed until the mission worked. That's not good gameplay.
I mean, the game's merits easily overshadowed its flaws, but the reverse-difficulty is a serious flaw.