lowyhong: Cosmic Encounter does look pretty fun. How luck-based is it?
There is a fair bit of luck. On your turn, you draw a card which indicates who you can attack this round. You can invite allies, the defender can do the same, then you both play a card to add to whatever total number of ships you have on your side. Attacker and all allies get a colony on the defender's planet if they win, with the defender and their allies losing their fleets to the warp. If the defender wins, their allies get bonus cards and the attacker and their allies lose their committed ships. Next player, start again. Go until someone has 5 colonies.
What really throws the game for a loop are the alien powers. There are 50 of them in the base game, and they all change the game a bit. Each player gets one (or more than one if you want to stack a few per person), and they can have massive impact on the game. It does imbalance things, but in a way that forces the other players to change up their tactics in response. The negotiation during alliance forming and the like are also a big piece of the game, since both the attacker and defender will often both try to get help from the same person. You can offer bribes and the like, so that comes in to it. And there IS the chance both the attacker and defender will play a Negotiate card, rather than an attack. In that case, they get one minute to come to an agreement involving any commodities/resources in the game. But maybe the attacker SAYS he'll play a Negotiate card, only to get the defender to do so so that his attack card is now an automatic win. But maybe the defender knows that, so now he'll play an attack card...it becomes a bit of a poker match, too.
The first expansion lets you play with up to 6 people (base game supports 5), and adds a rewards deck of higher powered cards that the allies of defenders get to choose from when their side wins a battle. The second lets you play with 7 (if you have both expansions, 6 otherwise) and adds a Hazard deck that throws random events in on certain card draws. The third lets you play with 8 (if you have all 3 expansions), and also gives you the option of playing in teams. All 3 also add another 20 aliens.
What it comes down to for Cosmic is what kind of group you play with. If you and your friends tend to have a lot of table chatter, and you enjoy some backstabbing and the like, this game will go over huge. If you're a quieter group that doesn't like confrontational games at all, I'd say avoid it.