For me the #1 goes to the original UFO: Enemy Unknown.
I think it's a perfect game. I can't imagine another game trying to do what it does surpassing it. It's a practically perfect realisation of its premise. There's a setting, a premise, goals, tools, options, freedom. It all works together. Everything you do in this game feels right and reasonable and compelling. Stakes are always high, goals are always clear, options are always open.
It's easier to see this game as perfect because in addition to various attempts at successors, it also got a spiritual 'remake' which completely betrayed the spirit of the original and made plain in many ways why the original works and is timeless. There's a perfect internal sense and harmony to how everything works in the original game which is completely betrayed by the remake. The original, despite being ancient, works on logic that feels perfectly sound and intuitive. It's all "of course I would do that, it makes sense to". Shoot things until they die. Bring as much stuff as humanly possible to conflicts to win. Playing the original X-Com *well* makes you do things which make sense. In all of my years of playing I've never found a true *cheese* tactic in X-Com. If something works it's because it makes sense.
In contrast, in the remake once people worked out more efficient ways to play the game became completely gay because optimal play looks nothing like the cool operator experience the game is meant to be, because the game's systems aren't robust enough to enable ostensibly sensible ideas to work. Getting good at the original game is about honing an organic sense for how to carry out a smallish scale gunfight at a decent level of fidelity. We aren't running a hard simulation of reality, but it feels like a simplified version of how such a scenario
*ought to work*. Getting good at the remake is not about what *ought to work*, the game is very particular, rigid, and fussy about what does and does not work. It's logic is very rigid, and very simple. It has *VERY BIG BLIND SPOTS*. Once discovered, playing the game *well* revolves entirely around these blind spots. And so it's now hideously boring and an inharmonious experience. The original game is a lower fidelity simulation of a war against aliens. The new game is a war against game mechanics.
This is my idea of what really makes a game great. This harmony. Is everything about the game pulling towards the realisation of the same vision? You don't have to dislike the vision, but is the work well realised? In my opinion no strategy game has realised this harmony better ever since. For strategy games if I'm not playing X-Com I'm probably playing modding X-Com. That's the other amazing thing. The screenshot above is from a mod, 'The X-Com Files'. The game's wonderful balance of fidelity and accessibility makes it an outstanding platform for building other games. Over the years X-Com modding has progressed from fixing bugs in the original game to the creation of total conversion mods which play like entirely new successor games on the same foundation.
I have a few other favourite games, and I might write about them here in the future. A common theme is that they achieve my standard of realisation to a very high level as well. A tentative top 5 might be:
1: UFO: Enemy Unknown
2: Super Mario 64
3: Halo: Combat Evolved
4: Dead Rising
5: Pikmin