You can easily get Executor in skirmish by uncommenting a line or two in one of the XML files.
As for my impressions: I've only played GC, but it's excellent so far. Fighters still have an annoying tendancy to be overpowered: if Ackbar's ship can't scratch my SSD, then how do a few Y-wings bust the shields down to half and blow up 4 hardpoints?
But balance is a lot better. The Empire is finally doing what it should be able to do in the last game--steamroll enemies. The Rebels are finally being annoying buzzards and skipping through defenses, and the Consortium is just plain annoying. This is good.
I'm kind of underwhelmed with Executor. She's a gorgeous ship, but the hardpoints are so far apart that she can't really shoot anything. Something needs to be done about the range on that... Thrawn is fabulous, though, and the DSII is beyond compare.
I'm pleased at the voiceacting for Thrawn. The VA in TIE Fighter was subpar and did the voice all wrong, but the Thrawn voice in FoC is passable.
The new landmaps are fantastic. I was impressed when I had Vader waltz up to a ysalamiri tree just to see what would happen, and he got eaten by Vornskyrs. Hah! Whoops, there goes my Super Star Destroyer... but it was hilarious.
I haven't touched the campaign yet, mostly since I just really wanted to play the enhanced Empire. I suppose I should try the campaign, if only to see Eclipse.