First of all, a warning. This may end up quite long. If you can't be bothered or don't have time to read the whole thing, read this: Buy Mass Effect. If you like it, buy Mass Effect 2.
Here's the launch trailer for Mass Effect 2. It's possibly the best trailer for anything, ever.

Mass Effect 2 was released in the UK on January 29th. I hadn't played Mass Effect, and I figured that since my January exams had just ended it might be worth trying out (it's fairly cheap on Steam, so why not?). On the 16th of February I completed Mass Effect 2. Bioware have done themselves proud with this one.
You may have heard bad things about Mass Effect, perhaps complaints about clunky combat and floaty driving, but don't let that dissuade you, or worse, make you play Mass Effect 2 before the original. I cannot stress how important it is that ME2 lets you import your character from ME1. When I started up Mass Effect 2, and saw Commander Julia Shepard - my Shepard, the only Shepard - standing there, it really means something, and helps give the events of the game more impact. These things aren't just happening to generic protagonist #694, they're happening to you.
There are many great things about Mass Effect and Mass Effect 2, I won't try to list them all. The voice acting is superb, with only a few exceptions. The story of Mass Effect is excellent, better than that of ME2, but ME2 makes up for that with incredibly slick combat. The driving sections from Mass Effect are not present in ME2, which I can't decide if it's a good thing or not. Both games have a very cinematic feel - it could be a sci-fi movie (and a pretty good one at that) with a third-person shooter attached.
I'm not sure what else to say - I expect my experiences with the Mass Effect games were drastically different to those that you may have, and I don't want to spoil any epic moments in the game.

You might want a score out of 10, or you may want me to offer a comment on the gameplay (I played these games and they were good. Is that ok?). I can't give you one. Mass Effect and 2 (I consider them to be the same - one is not complete without the other, and neither are complete until Mass Effect 3 comes out) are just my kind of thing, and as such I absolutely adore them. I had a lot of fun, and if you want me to quantify fun then I'll give you 10 recommendations out of 10, and 70 hours of my life that I'm glad to have spent playing Mass Effect. Oh, and there's a song, too.

<3 Shepard.