Well, you could start by looking at a few of the other threads on these forums.
For example,
this thread has a useful discussion on comparing Java/Scala for performance, as well as making the important point that Scala is not a "faster Java", but a different tool that allows you to solve problems in a different way. Scala allows you to gain the benefits of functional programming e.g. for easier concurrency, while still taking advantage of everything Java and the JVM can offer.
The InfoQ website also has a couple of pieces by technical staff from the UK "Guardian" newspaper, explaining
why they decided to switch to Scala, and also reviewing their experience of
moving from Java to Scala (mostly).
There is a
book review of "Scala for the Impatient" here on the Ranch as well.
Incidentally, there is a free online version of the first edition of
Programming In Scala by Martin Odersky, although this is 4 years out of date. It will give you a thorough introduction to Scala, but it's pretty heavy going if you're just looking for a tutorial!
Finally, if you want to learn more about Scala from the man who invented it, there's still time to sign up for
Martin Odersky's free online Scala course via Coursera, which starts on 18 September and runs for 7 weeks.