Tried this on a whim because I wanted some RTS action and it looked cool.
Got sucked in for 4 hours the first night. Damn. It's certainly entertaining. Lots of different campaigns to go through too.
Performance has been mostly fine for me. I did get some temporary stutter and fps dips with a lot of units standing in formation in a same location, like 500. Oddly when they were in combat with around 300 enemies it was fine. I'm thinking it was a combination due to location... Many windmills near a river.
This is on my secondary PC which is still decent. 2500K @ 4.5 with a GTX 770 and 16gb ram + SSD. Haven't tried on primary yet to see if there's a difference for either CPU, GPU or both. I'll do that of it gets worse when I get into really massive amounts of troops.