I feel a little bad rating this a 4 since it's a Beta book. It's really hard writing on betas b/c material changes so frequently.
I liked the book a lot and thought it covered the topics of LINQ and EF pretty well. I think though, it was a bit too heavy into language features of C# 3.0 and VB 9.0. Yes, it's necessary to cover many of these in the context of LINQ but I think proportion wise, it was a bit too much there and a little light in other areas (for instance, unless I totally missed it, i didn't see anything about parallell LINQ). The coverage of EF was good, but I would love to have seen about 50 more pages.
Although it's small the content is right to the point however. They do a good job of discussing LINQ and EF and even showing some more advanced areas and I will say that if you read this book and understand it, you can get just about anywhere you want to be with LINQ. You can read it quickly and be up and running very quickly and that's the strength.
In all honesty, I should probably have given it a 5. My personal opinion is that it's not quite a 5 but definitely higher than a 4. If it were 10.00 cheaper, I probably would have went for the 5 - but it's not a cheap book for the size of it.
The authors did a great job in many areas and considering it's a beta release, they did a superb job.