Exellence in its purest form
Graphics- I thought the first Mass Effect had great graphics, and it still does to this day. Anyone who played the first Mass Effect, however, is aware of the technical issues from the first game such as inconsistent framerates and excessive pop-in. All that has been fixed in Mass Effect 2, however, the frame rate didn't drop once on me nor did I experience any pop-in whatsoever. I didn't have any visual glitches in the game (except for one time when Tali was floating, but she stopped after a couple of minutes, no harm done). Overall, the graphics were excellent. The art direction is also worth noting, it was all very well done, especially the view of the city on Ilium.
Gameplay- The gameplay has been vastly improved as well. The gunplay in the first game worked, but it wasn't anything amazing. Mass Effect 2, however, feels like a high quality third person shooter like Uncharted 2 or Gears. The side missions are all improved as well. The uncharted worlds in the first Mass Effect seemed to be cut and pasted from every world with no variation. Fortunately, Bioware fixed that and all the uncharted worlds have unique side missions that never get boring. One thing I will say about the uncharted worlds, however, is that the planet scanning process gets very long, boring, and tedious. Fortunately, you can buy an upgrade to make the scanning process faster, so its not a big problem. I also have another complaint, albeit a small one. The citadel in Mass Effect 2 seems alot smaller with far less to do as opposed to the citadel in the first Mass Effect. Maybe it's just me, but it seemed far smaller in size, I liked how big the citadel was in the first Mass Effect. Regardless, there is still so much to do on all the other worlds and the citadel that it's not a big problem at all.
Story- I thought the story in the first Mass Effect was great, the story in Mass Effect 2 is somehow better. I don't want to give away any major details, but Commander Shepard, the character from the first game, is continuing his fight with the Geth and the Reapers and ends up in the employment of pro-human organization Cerberus. How he joins Cerberus and what happens, I'll leave up to you to find out, but suffice it to say, the story is not to be missed. The story is great, but the characters really make the experience so great. I have never seen so many characters of such high quality all together in one game. If you played the first Mass Effect, you'll be happy to know that many characters from the first game make a return, you'll end up fighting with some as well, though I won't tell you who. The new characters are just as good as the old characters, especially Thane, a Drell assassin that you end up working with. Another great thing about the story is how your decisions from Mass Effect 1, assuming you played it, carry over into the second one. The story may not change drastically, but depending on the decisions you made, the experience most certainly will.
If you have the choice, I highly recommend playing the first Mass Effect before playing Mass Effect 2. Even if you can't, I highly recommend getting this game, I haven't got this much replay value from a game since Fallout 3, and that's saying something
Well done Bioware, you've made an absolutely fantastic game for the 360, and this comes from a PS3 fan