I think the main Dominion expansions that add "new rules" are Seaside and Alchemy. Intrigue adds more cards and a lot more player interaction, Prosperity adds more cards and lots of money - I was getting hands with 10, 12, 15 or more money to spend with no problem - but I don't recall too many new rules.
There's a free, no-frills, single player with AI version you can download and play to try all the decks, I can't remember its name but I can look for it if you want.
I got Simpsons Scene It [huge Simpsons fan] and Space Hulk: Death Angel for Christmas. Space Hulk is a lot of game in a little box, and plays 1-6 players co-op to travel through a spaceship infested with aliens. It's sort of a pain to set up, but actually plays pretty easily and in less than 45 min if people know how to play. You're somewhat limited, each combat team only has three actions to choose from [Attack, Support, Move/Activate], and you can't do the same one you did last turn; and each of them has some special feature [one character can attack three times, another team can counterattack as a defense], so there's definitely some strategy to it. So far I'm 1 and 1; victorious [with two marines left, out of six] in the solo, and got slammed in the final round of the two player game.
Simpsons Scene It is, well, exactly like it sounds.