Google announced some serious modifications to its music service late Wednesday, pulling out of beta and into the wild world of commerce. Tracks will now be available on the Android Market, and will offer a catalog of millions of songs.

Hooking in its social network, Google+, the company is also making it easy to share songs either publicly or with select groups through the network’s Circles feature, adding the all-important element of social music discovery.

Here’s how Google measures up against some of its biggest competitors on a few key points.

Price: Google Music is free, free, free and lets you store up to 20,000 songs. Apple’s cloud offering, iTunes in the Cloud, is free for up to 5GB of music, excluding what you’ve bought on iTunes, and requires $24.95 per year to match up to 25,000 non-iTunes songs. Amazon MP3 also gives you 5GB of music for free; you can upgrade to unlimited storage for $20 per year.

Spotify and Pandora have free options but don’t let you use your own music. The same goes for services such as Rdio and Mog, which recently introduced free models that have their own limits. Rdio has an ad-free, capped listening plan, and Mog has a novel model that lets you “refill” your music meter, granting you more listening time depending on how much you listen, share and use the service.

Social: Social is a huge part of what these online music services are trying to tap, and each service does it in its own way. Google has — no surprise -- decided to make its music shareable over Google+, which is either a boon or a barrier, depending on how much you and your friends use the service.

Still, you get a little more control over what you share than with the Facebook-connected Spotify, Pandora, Mog and Rdio, which show users every track their friends have explored. It’s a matter of taste here: Do you want to share everything you listen to with more people or curate your suggestions to a smaller crowd?

Recommendations: Google Music also has an interesting leg up on the competition in the way it recommends music. In addition to recommending tunes from your favored artists and hooking in the suggestions from your friends, Google also has a staff of music critics who will be contributing reviews and their own recommendations.

It’s a different approach than the standard industry model of algorithms. The only model like it is probably Rdio’s, since you can follow “influencers,” such as Pitchfork Media or Rdio itself, for recommendations from outside of your social circle. Pandora, of course, uses its own complex maze of algorithms to analyze the music you’re listening to and recommend artists that share the same essential DNA as your preferred tracks.

Variety: Google signed deals with three of the four major music labels for its launch, giving it a portfolio of about 13 million songs, execs said in Wednesday’s press conference. By comparison, Apple has 20 million songs, and Amazon MP3 has over 13 million. Mog has 11 million songs; Rdio has around 9 or 10 million; and Spotify has over 15 million.

In an interesting new feature, Google Music will let artists create their own pages a la MySpace -- and let them set their own prices. So that means that Google Music will likely be an indie music haven for unsigned artists trying to spread the word about their work.

Accessibility: Google Music will go anywhere the Internet does — given that you have the Google Music app or access to a browser. Apple’s mobile users are able to get access to Google Music through the Web, which is a workaround for those who like to cross platforms. There’s no desktop client like iTunes, though, so you’ll need access to the Web to make Google work.

Google Music will only let you listen to your music on one device at a time, however, so if you — for some reason — want to fire up your tunes on your cellphone and in your living room, you’re out of luck.

Bottom line: Google’s music service ideal if you’ve got an Android phone, use Google+ and are itching to get away from iTunes. Even if you’re not an Android addict, though, it’s worth a try. It’s free -- so there’s almost no barrier to entry -- and at the very least, it could be useful as yet another backup for your music library. Google hasn’t done anything revolutionary here, but, as it did with e-mail, the company has pulled together some basic features into a free and easy-to-use service.

Related stories:

Google opens Music service to everyone, adds store

Apple releases iTunes Match

Spotify releases ‘private listening’ feature