If you love a good storyline, this game is for you. Mass Effect immereses you in a living breathing galaxy with amazing attention to detail (particularly on facial movements). As well as having a great main storyline, there are loads of side missions and planets to explore as well. The combat system can feel slow, as you need to access a pop up menu to select weapons and "biotics", although this doesn't affect gameplay too much. It's still fun to use your team mates variety of powers. I would also recommend that if you are fairly new to RPG's you play Mass Effect with the strategy guide.
Overall, Mass effect is a great timewaster with plenty of replay value, a must buy. :)