Actually, I never did like Mass Effect 2 that much... It had the misfortune of having to stack up to Mass Effect 2 :/ the shooting was good, but not great, I personally preferred the powers from the first game. Gameplay over all was just average, but then again, Mass Effect 1 wasn't the best shooter anyway, so the biggest factor for me was story.
Both games were amazing when it came to dialogue and characterization, but comparing the two for overall plot is just not even fair dude. Mass Effect had a handful of massive bombshells dropped on you at all the right times, the pacing was near perfect in areas, the villains were creepy and or sympathetic when and where it was needed, and the only issue I had was that the whole Reaper thing was maybe brought in too early and overplayed... Anderson kind of made that stand out x.x but I played Virmire from start to finish in one sitting, without dying, so I've seen the game at its best.
Mass Effect 2, however... it nailed the small time stuff, like characters and optional story arcs, but the main plot had nothing on Mass Effect 1. There is no contest. None whatsoever.