I tried Mass Effect 1 myself. Only played through a few hours of it. For an RPG it bored me for a while, it was too easy to get trapped in the billion of side quests that had nothing to do with anything and get lost in the game. So I never really got to into it.
For Gears of War, I refused to play the 2nd one until I completed the 1st campaign, and I was happy with that decision in the end...
But will I need to really know what happens in ME1 or can I play ME2 and understand it. It looks much better than the original.