to be honest i didn't like the game at first because i started off by playing against a friend of mine who had played this game for a lot longer so because i didn't know what everything was and what to do with almost everything. so i suggest either playing the tutorials but if you want all the tricks and bits that the tutorial doesn't tell you, you should play the campaign mode. and to be on the safe side so that you know most of the tricks in the game i suggest playing all the campaign modes for all three factions so that you have some knowledge about all the factions.
once you have passed the lengthy learning curve then the game becomes much more fun and to be honest once you have played a good game on it then you don't really want to play any other rts, this game is so epic that it blows away every other rts. the main plus point is the number of units you can construct and also the size of the maps, it just makes the battles much more epic.
on a performance side it isn't as demanding with hardware as people say, at this point in technology we already have quad core however because this game was made before this time it will not use all 4 cores. however i have a laptop with and Nvidia 8600M GT and a intel core 2 duo 2.0GHz processor and 2GB RAM. this is enough to play the game in complete full graphics, so i can turn all my settings to the highest possible settings and the game will run smooth. the only problem is that the laptop/desktop gets very hot after around 3hrs so a cooling device is suggested.
This game is much more though compared to other rts games in the time sense, to get the game going(in skirmish) you have to put some time in building your resources and then your defences and then you will want to also upgrade your buildings such as factories and shields and defences. then you will want to think about major defences to repel enemy attacks and then you will want to build your own attacks. and basically a well played game lasts around 3 - 3.5 Hrs. a long time, yes, however it gets very addictive and you need to make sure you take breaks.
The one thing that i suggest you do not do is:
DO NOT BUILD NUCLEAR LAUNCHERS AND FIRE THEM AT THE ENEMY, IT WILL JUST MAKE THE GAME BORING!!
but by all means build strategic missile defence's to counter the AI's nukes.
so overall the game is ridiculously awesome, and is so epic that any other rts will seem boring, smaller, and it will stay as one of the best rts for some time i think.