I played the first one alot, wasn't too good at rts's when I was playing it (still am not that good at them lol) so I never really played online. Favorite RTS so far was definitely Rome total war though, so I'm definitely gonna check out Empire... sooner or later.
Now that I think about all the rts's I've played Empire at War's space battles were loads of fun, but maybe that's just because I like star wars.
"An Air Force A-10 Thunderbolt II flew a show of force and expended flares for emphasis over Salerno after enemy forces attacked a coalition forward base. The arrival of the aircraft prompted an immediate retreat by enemy personnel."