It's taken some time before some user reviews of CI finally surfaced.
Gerald Katz posted one on the rec.boardgames.ce newsgroup- mostly positive:
"Hooray for the return of Kickers, Negative Attack Cards, and some
Edicts (Artifacts) like Space Junk and Hand Zap.
I like the crooked Negotiates. +1 compensation or -1/+1 ship to the
warp on failed deal..."
Nate Owens posted an even glowier review on boardgamegeek:
"It’s a welcome expansion, and the extra variety is so good, I would recommend this expansion be bought when you pick up the base game."
Of course, I'm pretty biased when it comes to Cosmic Incursion, but I think it's a fantastic addition to CE, and I highly recommend it. The 6th player color let's you have a bigger and more intense game- or you can just use the ships to play with Symbiote in a 5 player game.
The 20 aliens are a great mix of old a new. Sniveler was one of the most requested classic alien, and it's joined by several others I've always been fond of (Chronos, Seeker, and Plant).
Finally, I've been a long advocate of the Reward Deck (naturally). I like the fact that it makes defensive alliances an even more serious consideration for all players. While not everything in the Reward Deck is great, the lure is often too hard to resist. The first game I played with CI, I drew four rewards (all of the negative cards and a negotiate). It was a serious bust. But since I was playing Ghoul, I was tapping into the Reward Deck a lot, so the next time I ended up drawing a pair of artifacts, a kicker, and a high attack card. It's worth the gamble.
If you love Cosmic Encounter, then this expansion is a must. Even if you only like CE, I think the expansion adds quite a bit and will enrich your experience. We're less than a year away from the next expansion, which I'm eagerly awaiting... if it's in the same league as CI, it will be another great addition.