A common trope about the newest Mac operating system, which came out today, is that it's not too different from its predecessor, Lion -- even in name -- so, why upgrade at all? It only costs $20, so it's not as big a purchase as in the past. And, thanks to our expert Mountain Lion reviewers, who have spent the last week or so with the OS, we have some answers as to whether it's worth a dinner for two at Chili's. 

First things first, $20 gets users a more polished version of Lion with some added features, which Apple announced during the Worldwide Developers Conference last month, as Daring Fireball's John Gruber explains.

In short: a nicer, more polished version of Lion. There’s definitely new stuff: iCloud document storage (more on that in a bit), Messages (which is more than just a renamed version of iChat — it supports iMessage), Notification Center (which I really like on the Mac; it’s perhaps the feature I’ve missed the most over the last few months testing the Mountain Lion betas when going back to my main machine running Lion). More back-to-the-Mac stuff from iOS, like standalone apps for Notes and Reminders, and convenient system-wide “share sheets” for sending content via email or messages and to websites like Flickr, Twitter, Vimeo, and soon, Facebook. (Facebook integration is not included in OS X 10.8; Apple says it will come in a software update “this fall”.) AirPlay Mirroring is a gem of a feature — a shining example of Apple’s “all our stuff works together seamlessly” philosophy. The new voice dictation feature is accurate, simple, and convenient — a huge accessibility win for anyone who has trouble typing.

"Polished" means a better, faster, cleaner version of the former OS, TechCrunch's MG Siegler clarifies.

It’s definitely the most polished and robust version of OS X yet. If you liked Lion, you’ll love Mountain Lion. If you didn’t like Lion, you’ll probably love Mountain Lion even more because it seems to fix a lot of the performance/quirkiness issues that some folks were having with the last version of OS X.

Though, Gizmodo's Jesus Diaz doesn't quite agree, arguing that "polished" only applies to speed and performance and not interface issues. 

While usable and fast in the newest hardware, this version doesn't solve the clusterf*ck of interface concepts introduced in OS X 10.7 Lion. It's just adds some nice stuff—like a convenient Notification Center lifted from iOS or better Cloud integration—while keeping all its many sins.

As for the feature updates, there are actually over 200, but the majority of them aren't too huge, explains The New York Times's David Pogue

Now, Apple claims “over 200 new features.” But some of them are tiny tweaks (Safari checks for software updates every day! Ooh!) or techie-only treats (“Xsan, the high-performance cluster file system”). Fifteen are improvements for Chinese customers, which is great for Apple’s world-domination plans but irrelevant to non-Chinese speakers.

So how many are real steps forward?

Gizmodo's Kyle Wagner likes Safari, for example. 

In addition to all the other Safari-only and Safari-friendlier features, the new tab switching is really good. You pinch with two fingers when you're all the way zoomed out on a page (which you should be by default), and you enter a screen that lets you scroll between all of your tabs quickly, with visual previews of each page. It's very lightweight, fast, and responsive.

AllThingsD's Katherine Boehret got "completely addicted" to the new share sheets.

I got completely addicted to Mountain Lion’s Share sheets, which pop up whenever you’d hope to be able to share something. This includes Web pages from Apple’s Safari Web browser, and items from Apple’s Notes program or photos that you want to send to friends. Share sheets use whimsical animations to bring a paper clip, photo and text together on a little piece of virtual paper that gets whooshed off into the ether. Sharing works through a variety of methods, so you can be sure to reach anyone.

Pogue found the iCloud integration "magical." 

All of these sync with other Apple machines wirelessly, courtesy of Apple’s free, increasingly sophisticated iCloud service. The new apps join Mail, Calendar (formerly called iCal) and Contacts (formerly Address Book), which already sync with your iGadgets. Change a phone number on your phone, and it’s instantly updated on your tablet and computer; set up a reminder on your Mac, and your phone will chirp at the appointed time or even place.

Diaz calls the Notification center his favorite update.

My favorite thing about Mountain Lion is the Notification Center, a live-updated panel that hides on the right side of your screen. If you have an iPhone or iPad with iOS 5, you know how it works: When a new email, Twitter DM, or any other alert comes in, a notification briefly blips onto your screen. 

Though, his colleague Wagner points out a feature flaw.

OK, so the notifications panel is pretty nice overall. And the alerts for new Messages and Emails are especially good. But it's all finicky. Sometimes an email will get stuck in the notifications panel, even after you've read it. Other times you'll get a Messages notification for an IM you received 10 minutes ago, instead of one you just got, or when nothing happened at all.

Is it worth it? Yes, says Endgadget's Brian Heater.

Let's get this out of the way, shall we? Does Mountain Lion justify its $20 price tag? Yes. Of course it does. If you're an OS X user with a reasonably new piece of hardware, stop what you're doing and upgrade now. There are 200 features here -- odds are you're going to discover a couple you like. 

For the following features alone it is a value, adds The Loop's Jim Dalrymple.

Mountain Lion costs $19.99 and comes with more than 200 new features — that’s a bargain at twice the price.

The new features aren’t just eye candy that you’ll use once or twice and then forget, either. Gatekeeper, AirPlay Mirroring, Facebook and Twitter integration, Power Nap and Notification Center all make Mountain Lion the easiest, most secure and most efficient operating system that Apple has ever released.

And after his 25,000 word, 24-page review Ars Technica's John Saracusa says yes, too.

Nevertheless, my advice is the same has it has been for the last several major releases of OS X. Mountain Lion is a better OS than Lion. It's also inexpensive, and you can purchase, download, and install it the second you finish reading this review. But before you do, make sure you have a good backup of your entire system. And if you're at all concerned about a disruption to your work due to OS bugs or application incompatibilities, there's no harm in waiting a few weeks to upgrade.

But, we do have one dissenter. Even at $20, Diaz says no.

Even at $20, most consumers will not find Mountain Lion worth the upgrade. And it doesn't seem to speed up your Mac. People looking for things like Twitter integration and Cloud storage should get it. Everyone else, you can save your coins.