I just remember that feeling when playing my first game of Dominion ever, and looking at all the cards and seeing the one that gave you +1 of everything, and thinking, "Man, that card is AMAZING."
Then I bought like 2 of them along with other random terminals and got crushed. Welcome to Dominion.
With what we know now, Market is very okay. It's a great source of +Buy, and on the right boards, can be a pretty impressive card, or at least an important component in a strong strategy. But there are so many boards where it seems like it might be good, and there are just more important things to get with your $5.
It's fun with stuff like University and Altar where you are gaining $5 cards left and right anyway, and hey, Market is a $5 card, let's have one of those. This works especially well against bots.