I know nothing about this series; my RTS experience is stuff like Company of Heroes, Dawn of War 2, Grey Goo, etc
What makes these C&C games classic/special/good?
I forgot to answer this.
What makes these games special to me, outside of the love and nostalgia I have for them, is its unique mix of mechanics and pacing. This is a game where you need to build a base, acquire ressources, build and army and just go and wreck shit. Another franchise that is the closest to what C&C offers is Star Craft, but even that, there's just something a little different about how it feels.
Starting with Red Alert 1 and going forward, mission get more complex. Often times, you start a mission with units but no base, and you must accomplish objectives using these limited means before being given a construction yard. It gives missions variety and gives the player a sense of progression and accomplishment.
Imagine a mission where you are given a commando with some support units, and your objective is to go and cripple a small base. You navigate a map, take out some units using various stragegy, all the while a mix of moody or upbeat music plays, then you reach the base a cripple it. At that moment, the map expands greatly, you are given the objective to destroy the real enemy base, and you are given a contruction yard to accomplish that.
That moment, right there, is like moving on from foreplay to the good stuff. What succeeds the infiltration mission is great by itself, but is enhanced by the infiltration mission. It's just good mission design. And you get to experience that with the addition of a cool stories told through neat FMVs.
The Westwood games all share the same DNA, but all have a different signature, if we could call it that. C&C1 and Red Alert have a mix of atmospheric and frantic tone, while Tiberian Sun leans more into the atmospheric and moody, and while Red Alert 2 leans more into the frantic and adrenaline rush.
If you want to give the franchise a shot (and I greatly recommend that you do), you are in luck because you have several free options at your disposal:
OpenRA -- OpenRA is a fan remake of three Westwood games that were made freeware by EA years ago: Dune 2000, C&C1 and Red Alert 1. The devs behind it are using a brand new open-source engine that offers modern features, rebalanced units, and it just runs better than the old games. The game actually still plays superior to the new remaster for these reasons. The single-player campaigns are not complete yet, and they are missing connective tissue between their missions, but what's there is solid.
You can get OpenRA here.
Tiberian Sun -- Tiberian Sun was also made freeware back in 2010 by EA. Fans have taken it and modified it to run on modern systems. It's the complete game.
You can get it here.
I recommend you give Tiberian Sun a shot first. It's more modern and elaborate in its design than the first two games. If you want to try the first two games, go with Red Alert first. It's more elaborate and better-designed than the first game.