BioWare is known for truly spectacular stories, and I must say that Mass Effect delivers. You are free to forge Shepard as a paragon of goodness or a renegade badass. Clearly I played the evil path, or Renegade. There were moments of the story that really hit home. It will come as no surprise to those who have played any BioWare game that your companions may not stay with you through the whole story. Losing someone who has been with you through thick and thin, especially the way I lost mine. I won't include any spoilers, but BioWare did an excellent job in writing the painful moments of losing friends.
The different alien races are pretty cool, and their relationships with each other in the universe. There was nothing like elves in Dragon Age where I really connected with the race and their situation. Krogans really have the short stick of the universe though. That genophage thing is pretty messed up.
Combat is decent, although very scattered. I would enter a fight and randomly die, retry the same strategy, and win super hard. The class I chose was pretty fun, relying on shotguns and pistols. Grenades feel largely useless at times. I also hate that as a class that can't effectively use Assault Rifles or Sniper Rifles, I still had them permanently equipped, making quickly scrolling between my 2 weapons somewhat frustrating.
There are some segements where you drive a tank, which are a bit painful. YOu blow everything away and are rarely challenged. Fortunately these parts or short, and broken up by excellent on-foot combat and story cinematics.
I didn't do anything with companion affection, and honestly don't even know how it works. In Dragon Age and Star Wars: The Old Republic, companion affection just happens. I didn't even notice my companions caring what I did in Mass Effect, which was disappointing.
The RPG elements felt a bit forced. I could go into a bunch of different abilities and improve them, and my companions as well. I tried setting up the Holy Trinity with myself tanking, Wrex DPSing, and Garrus healing, but there are no threat tables or anything, so it was a crapshoot whether I took a sniper bullet in my extremely well shielded self, or it wrecked poor Garrus. Also "healing" is a joke. But I succeeded somehow.
Overall, story was incredible, combat was good, but some auxilliary elements felt lacking. I suggest you play this gem of a game, if only for the amazing story.