Edit: I gave it another chance, and had a lot of fun. I still say Invisible Goblins are heavy handed, and not very thematic, so in the future I'm house ruling them like a trap. If a party member detects them, nothing is stolen, they harmlessly run away, and the party gets an XP roll. Theives and halflings get +1 on the detect roll vs. a 5. After all, invisibility does not also grant complete silence, and if the characters are alerted, there's no way they're going to steal everything and escape. A) The item they are holding is not invisible, even if they are. B) If the characters can see their items floating through the air, they can attack, and chase the goblins. I think this is more fair than the rule as written.
Upgrading from a 2 to a 4.
Downloaded, and read the rules, sat down to play the first game. Invisible Goblins stole all weapons from the party in the 3rd room. It's not possible to fight the Invisible Goblins, or avoid them. I did not find this very enjoyable, by I may play again some day.
[4 of 5 Stars!]