Are the Mass Effect Books Any Good?

I thought Mass Effect 2's story was pretty excellent. Can anyone tell me if the books are worth reading?

They aren't the greatest piece of literature, but if you are really interested in the universe, like me, they are good books to read. 
Also, you may need an interest level of more than "I'm kind of interested in the universe," and more like "I've read every codex entry in both Mass Effects" to truly enjoy the books.
 
Out of the two I've read (I'll be reading the third soon enough) the first one is the better of the two.

I've read Revelations and Retribution should be arriving on my doorstep sometime this week. As far as Revelations goes, I think it's brilliant. I found that Saren was by far the most interesting character in Mass Effect, and when the information parts with Saren in the book are great. You should totally go for it. I have to ask though, have you played through Mass Effect 1? Because if not, the book doesn't really do much.  
The reason why I was so interested in Revelations was because when ME1 hinted that there was history between Saren and Anderson, and Revelations fleshes out said history. But if you haven't played Mass Effect 1, I don't think the book will really do much for you, because Mass Effect 2 SERIOUSLY lacked Saren, and I was very disappointed.
 
I have the same rationale for Retribution as well. I love The Illusive Man's character and I want to dive more and more into his world. Since you have finished Mass Effect 2, you might have a better time with Retribution since you do possess the context.

Basically what h8er said, the first is pretty interesting provided you played the first game, I have't read the second so can't say on that one.

I've read Revelations and Retribution. Both were great. Revelations was fantastic actually, and it directly ties into the story, so it's not some side story.

I'm sure they're fine books, but there is much better hard SciFi out their. 
I would pick up either some Clarke or Asimov. 
I highly recommend I, Robot by Asimov and Childhood's End by Clarke. 

The first book was cool because Saren is a badass, the second one was dull as hell. Haven't read the third one.

" I've read Revelations and Retribution. Both were great. Revelations was fantastic actually, and it directly ties into the story, so it's not some side story. "

I was just looking, within the last week, to pick up the Mass Effect books since my local library doesn't have them.  This is good to know, even though I'd probably just get both since they're sub 9 bucks.

I read the first one back when the first mass effect was brand new. I enjoyed it quite a bit. Drew Karpyshyn fills in some really interesting back story. I haven't read the second one so I can't really comment on it.

What's the plot of Revelations?

The books do a good job of filling in some of the back story.  They aren't necessary to play the games, but I found them to be very helpful in understanding the different character's motivations. 
 
Revelations is basically the backstory of Captain Anderson and his connection with Saren, the Rogue Spectre from ME1.

I read the first two ME books, and they accomplished the task of delivering more Mass Effect. However, the stories themselves weren't super memorable, but passable as quick and dirty sci-fi reads.  I'm interested in the third novel because from the synopsis on the back of the novel, it seemed to me that it may be about the Reapers and the Illusive Man.  I may try to get into the book this winter or next summer, hopefully before the third game comes out.