This is very interesting to read for me, as I think Red Alert 3 is my personal favorite, being a lifetime CnC fan myself.
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I actually like the way they streamlined the economy system. Don't get me wrong, harvesters are a fun and perfectly fine system, but the ore nodes encourage people to play around them, planning expansions, defense, harassment, etc. The game's economy isnt as explosive as RA2's, or even KW's, but that allows for more calculated and frugal playing that isnt found in those games. Every unit; every structure matters. RA2 is more fun in a casual setting yeah, but lets be real for a moment, spamming tanks and ore miners can be fun only for so long.
Abilities and extra micro options for your units makes what used to be a 4v4 ring-around-the-rosie, into an interesting scenario to turn the tides in whatever fashion you can. For example, Hammers are more powerful than tsunamis, but those tsunamis can still win that less favored engagement with proper use of reverse move and nano deflectors. But lets say, Lashers vs Rhinos? Unless you screw up big time, the rhinos will win, every time.
Competitive play was focused on big time, as you say, but it payed off and offers a unique experience for the people willing to sink their teeth into it; RA3 offers a different kind of skill expression that you can't get out of other CnC games, or even other RTS games either (like...starcraft...2

).
But RA3 has great moments for casual play as well. The co-op campaign was tons of fun, even on your own, and it was still a pretty typical story for a red alert game, even if it was a little sillier (the game itself is also pretty goofy, but I like that

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Some other small things, the games OST is great, and the game itself looks fantastic, considering the fact that it was released in 2008 (a rushed release, at that). Also we're just gonna act like chronosphereing mirage tanks, or IFV tanya isnt gonna melt a base in seconds? Or that submarines (especially boomers) aren't BS units in RA2 (granted that naval combat isnt as important)?
If you're interested, I'd recommend a few videos from XYHC, who explained this game's design philosophy in depth. Very good watches, if you haven't seen them already.
(All CnC games have tons of redeeming qualities, EXCEPT CnC4, or the mobile games, IMO

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