Mass Effect is just one of those few games that, despite numerous issues, rises above them to become truly amazing.
Now Im going to get this out of the way, Mass Effect has MANY, many, many flaws. From the framerate issues (where the game just slows down to single digits even sometimes), various bugs (especially when driving the mako), graphics that occasionally pop in and out of high detail (think Halo 2) and the vehicle portions of the game. That said, there is not a better story or world in all of gaming.
Constantly the game throws surprises at you. Even when you think everything is figured out and set in stone, even at the very final minutes of the game, the game throws surprises at you. To put it plainly without spoiling anything, you are a handpicked soldier who must stop a rogue SPECTER (think spy in space) named Saren.
The game also brings up the morality and choices issues like in Kotor, but they aren't limited to just good and bad. Yes there is a morality meter but they don't measure your good and evil, so much as if you have the ability to say as good or evil things in conversations. Also, this lets choices become much more ambiguous verses good or bad meaning just actions and consequences.
Speaking of choices, the game has a lot of them. In kotor, you had mainly one big decision and turning point at the end of the game and that was it. What you did before didn't matter so much as what you did at that moment. In Mass Effect, you can practically change the entire world and almost everything until it becomes what you have shaped over the course of the game. There is no large "good or bad" decision's you make at the end. There is no Good ending Bad ending, just a large shade of gray.
What really amazes me about Mass Effect is that despite the numerous issues that would absolutely destroy any other game, it just doesnt seem to matter as much. All the bad things are really cast down and overshadowed by all of the good, and considering that sometimes I had to reload an entire area because of some bug they were pretty bad .This is one of the best games of the year and in my opinion, the best game of the year.