What is a beta reader for? They just read the story and tell you what you think, right? Isn't that the same as a review?
At this stage in the game, no. What they do at this point is much more important. These readers aren't doing this to edit for you, though some may point out the more obvious errors. Beta readers are for pointing out serious mistakes in the manuscript while you still have time to fix them.
Beta readers are readers. First and foremost, and as such, at this stage of the game, they're pointing out things which make them stop and put the book down. Things like characters appearances changing, or characters not acting in ways consistent with how they've been described. Holes in the plot. Loose threads which seem important but that are just left dangling. Twists which are so out of the blue, it's like a shark just attacked them in their own hallway.
(Because that just makes ALL the sense in the world.)
Beta readers are there to tell you the things in your story that just. Don't. Work. It may be hard to listen to them at times, because they may point out that the whole sub-plot from page 24 through page 317 makes no sense; something which would require a major rewrite to fix. But that is exactly the point. These are the things which will flat out kill a book that they're trying to point out to you. Things you will need to fix before your next great work heads to a professional editor for a grammar and punctuation cleaning.
That being said, there are different levels of beta readers. You have your close friends and family, who are likely to tell you that everything is awesome and not to change a thing. Enjoy the praise, but don't trust it. After all, these are the people that want to see you happy and to see you succeed more than anything and they're likely to overlook discrepancies in order to tell you what they think will make you happy.
That doesn't mean you shouldn't ask them to take a look and tell you what they think, it means you need to be prepared when you approach them. Include a list of questions for them to answer when they've finished reading. Questions like: "Did you like the main character?" "Did the scene on page 154 make sense?" "How scary was the scene on page 243?". Specific questions make it easier for them to mention and talk about things that didn't work for them, as it lets them know that you're aware there might be issues without putting them on the spot to pick things out on their own.
After close friends and family, you have people that you know and trust, but that may not be so attached to you personally. These include experts in fields that your book contains, people you've come into contact with professionally, maybe people you consulted on certain subjects for your book, and that have a personal interest in making sure you have your details right. These are the people who, while likely to still be able to tell you that your main character is unlikable and they were waiting for him to die, are going to point out things like whether Ford made Escorts in 1978. It really can be a detail that small which rips someone out of your book with enough force that they won't go back to it.
Then you have professional beta readers. Some editors offer this service in addition to working on the punctuation, but make sure you don't get the two things confused. These are two completely different steps in the publishing process. These are the best you can do for a good beta experience, although they aren't free, you usually get a written report after they've gone over the work, explaining what worked well, what didn't work at all, and depending on the service, you may even get a list of suggestions to fix the issues they found.
So what comes after all this? More revisions. You listen to what the beta readers have to say, see if comments line up along multiple beta readers (You should at least have three to four, though I would say not more than seven, that way you have a tiebreaker if you need one). If the book needs a minor touch-up, great. More often than not though, you're going to be looking at a rewrite or two. An additional scene to get a particular relationship across, maybe re-write a scene so that your main character's actions make more sense or so he's more likable.
Remember, this is all for the betterment of your book, so keep at it. Don't fret! Even if your work requires some major work, every step forward is a step closer to the end, and the end is almost in sight.