Mass Effect is Bioware's game, so story is quite good and has the usual good or bad thing, would you rather listen people whining or shoot them in the face ect.
Combat is like Gears of Wars mixed with KOTOR, you take cover and shoot the enemy, you also have 2 other guys with you and the ai controls them. Guns don't have ammo but they overheat, you can do magic like attacks, you can pause the combat and have this tactical view in where you can give orders/use special abilities ect. It's a nice change from the usual watching automated attacks and just giving special ability orders.
Ending is really good and opens new room for a sequel, which comes out in next month. This is a good time to play it.
If you just play the story and ignore the side quests it takes around 12-18 hours to finish.
Once you get past the boring start the game has a lot of depth in it. It just pulls you in its world and the time just flies when you play it. Couple of hours in the game and I found that I can't stop playing it, it really is that good. This is one of those rare games that can do that to you. It's not that hard as Dragon Age is, so this one is a nice relatively easy ride from start to finish.