I agree that the exploration in Mass Effect was pretty terrible. Maybe in the second one all those boring pre-terraformed planets will be more interesting.
As for the whole first game being a prologue... I guess I can agree to a degree (har har rhyming). Mass Effect 1 did spend a lot of time just giving the player a feel for the universe, all the different species and politics and things. In retrospect, it feels a lot like the pilot episode for a new TV show.
I still think that the first Mass Effect was a lot of fun to play. And if the second one is 10000 times better, then GOOD. That means it will be a SUPER AWESOME game.