First, there are two different versions to consider.
The basic MLB.TV service, at $110 for the year or $20 a month, offers full HD games, Live Game DVR controls, Audio overlay, Full Game Archives, a Fantasy Tracker and a Mosaic view to watch up to 4 games on the same screen. The ability to go back and watch an exciting game if you missed it the first time is an underrated bonus to this service. It's also ridiculously cool to watch 4 games at the same freakin' time!
MLB.TV Premium, at $130 for the year or $25 a month, offers 3 huge upgrades over the basic service.
Most importantly, you can only use MLB.TV on connected devices with the Premium membership. This means if you plan on watching games on your smartphone, tablet, Playstation 3, XBox 360, Roku, Apple TV or other devices, you must have Premium. Otherwise, you can only watch the games on your computer. That alone is enough to pay an extra $20 for the season. The supreme flexibility of watching games almost anywhere is a huge reason for the popularity of the service.
But there are two other perks to spend a little more moola. You get MLB At Bat for free with a Premium subscription and access to Home and Away broadcasts. MLB At Bat is really cool. By itself, for $20, you can listen to every baseball game through home, away, or Spanish broadcasts. To be able to watch any game on your phone over wifi or cellular data, you need the Premium subscription. Using data, you're not going to get the crystal clear picture quality on your iPhone, but if something exciting is about to happen, you'll be glad to have a video feed.
But here's the rub (quoting Mad Eye Moody). If your TV provider has your favorite team available in your area, MLB.TV is not worth the price because of blackouts. But no matter what, MLB At Bat is a MUST have for all baseball fans, simply because it is the only (non-jailbreak) method to listen to baseball games on your phone.
Let's say your team is on CBS radio and you listen to other programs from the station on your smartphone. When it's game time, the app will cycle back to another program. There's no way around it. It's $20 for the entire season of listening to any game for any team on your phone, along with NO BLACKOUT restrictions. And the At Bat app has a very polished interface which provides line scores, news articles, video highlights and complete roster breakdowns.
I'll resist MLB.TV because I already get the TV station for my favorite team. But I'll probably buy it later in the season when it's discounted or in September during the final race to the finish line. But MLB At Bat is essential and you're not American if you don't buy it....unless you really don't care for baseball....hot dogs....apple pie....or Chevrolet.