For some of us on Windows 7, a few things need to be done to get this to work correctly. I don't know if this affects just the 64-bit version (which is what I run on), but I had trouble getting this to run after purchasing it via Steam.
If you attempt to run the game and nothing ever shows up (even though the hard drive thrashes), the game is definitely crashing. I've looked in the application log and found that the executable is causing a crash to occur. Whether or not you apply the 1.02 patch or not, the game will not run out of the box from Steam unless you do a few things.
First, from the Games tab, right click on Mass Effect and tell it to create icons on your desktop.
Next, right click on the Mass Effect icon and select properties. Go to the compatibility tab and tell it to run in the Vista SP1 or SP2 mode.
After that, double click on it and you should see the Mass Effect splash screen come up. Eventually, the screen will go black and depending on possibly your set up, it might sit at a black screen for a few minutes, but it will launch. At least, that's what happens for me.
I have the game running at 1280x1024 with all details on and it runs fairly smooth, even during the combat sequences. I just can't stand how it takes about 2 minutes for the game to launch.
I'm only 15 minutes into the game but I'm already enthralled by the story and can't wait to see what happens. Oh, and it looks gorgeous.
My machine isn't the best:
AMD X64 4200+
4 gigs of PC3200 RAM
ATI HD3870 Video Card
Windows 7 Professional 64-bit
SATA II hard drives
Yet, it still runs great once it's launched.