Yeah, but which version is better? I want whichever one has the most to do. I noticed one of them has ship fights, urban warfare, weapon/equip progression through research, etc.
Apoc is the coolest, the first has the best sense of Earth being invaded and to me the best grand strategy. Skip Finding Nemo the second one unless you are a superfan.
I'm with you on this one, Terror From the Deep can basically be described as a reskinned Enemy Unknown, with some additions and mostly just changes.
Technically, Terror from the Deep is a reskinned Enemy Unknown, except with a handful of new features, all of which are horribly bugged. A new research system that can be permanently broken in at least two different ways, Dye Grenades that do absolutely nothing, aliens equipped with melee weapons that the AI isn't trained to use...
Apocalypse is the one we keep talking about. The graphics are slightly less
eye-gouging retro, battles can optionally be fought in real-time instead of turn-based combat, there's a faction system, there's interesting UFO combat, the end-game is more involved... yeah, it's generally considered a slightly-unpolished gemstone, where as Enemy Unknown is considered a highly-tarnished and very rough diamond the size of your head - awesome concept, but honestly, a lackluster execution.
But yeah, Apocalypse is $5.00, and totally worth picking up. Add on Enemy Unknown if you want to spend $10. The full pack probably isn't worth it - it's effectively 2 free games, but the two games in question are Interceptor and Enforcer, which are terrible.
You forgot harder.
Only if you don't get a version that fixes the infamous 'difficulty bug', wherein all Enemy Unknown games reset to 'Beginner' difficulty once the game is saved or a battle ends. I've heard some of the latest versions fix this... at which point the games are pretty much reskins of each other.