Siri is good for a little note or something, but lacks good punctuation.
It's totally subjective though, and everyone has different experiences. Your sig says you have an iPhone 5, why don't you try it out? Why are you asking?
Not sure what we can really tell you. Siri is a neat feature but it doesn't always work well. There isn't much you can do if Siri doesn't work well for you or recognize your voice well.
Is siri compatible with your native tongue? You might find better results just using Siri in your native language.