Recently, I played a few old RTS games (Tiberian Dawn, Tiberian Sun) and a few more recent ones (Red Alert 3, Grey Goo) and I was struck by how differently paced they are.
In the old games, everything happens slowly. You accumulate resources slowly. You build units slowly. Your units trundle across the map slowly. In Tiberian Dawn, for example, building even a single medium tank is a significant investment of time and money. Building a second tiberium refinery can effectively double your income, but it also means making yourself vulnerable for a long time if your opponent decides to put that initial investment into a rush instead. Everything happens slowly enough that you have time to act deliberately, and every action feels worth deliberating.
New RTS games, by contrast, feel like anxiety simulators to me. You rack up resources quickly. You churn through your build queues quickly. Units charge across the map. There's never enough time to do all the things I need to do. Oops, I tried to use proper combined arms tactics to assault an enemy base, but that stole my attention away from my build queue, causing me to ram my resource cap and now I'm pissing away credits. Oops, I tried to get my build queue in order and in the process my unit blob was left vulnerable and now the enemy's flanked me and destroyed my artillery. Oops, I tried to set up base defenses and while I was doing that my enemy beat me to that highly contested resource field by a few seconds.
When I lose in an old RTS, I feel like it's because I wasn't clever enough. When I lose in a new RTS, I feel like it's because I wasn't fast enough.
Peak RTS for me is either the original Homeworld or Rome: Total War, both for different reasons.
In Homeworld you tend to build up your forces while lumbering through the map from objective to objective, launching little raids with your strike craft against your opponent's resource while scouting their unit comp so that you can add the appropriate counters to your fleet, and then the match ends in a glorious orgy of violence where you get to see who did it better.
Rome tends to start with the orgy of violence, where your best units square off with your opponent's and then depending on your initial deployment you will probably win in one area and lose in another, making the mid- and late-game about reacting appropriately to changing conditions.
And both games got worse in their sequels by adding a bunch of special abilities and other unnecessary fluff. No, I don't want whether I win or lose to be determined by whether or not I pressed the "increase damage" button at the optimal time, I want it to be because my bombers went uncountered and cleaned house against the enemy battleships!