Emphasis is the difference. Nuance can be difficult to distinguish for non-native speakers learning the nuance and developing those instincts in a foreign language. With respect to English, using phrases such as "came as a surprise" or "came as a shock" can show the speaker's intention to stress that suprise or shock. Also, when those phrases are used, you'll often find the speaker's speed and intonation - in other words, their behavior - will change. To identify something with the particles "was" or "is" is the minimum required to make the sentence. 強調する表現を考えています。例えば、翻訳ではありませんが、「驚きました。」は「すごく驚きました。」になったら、どんなに驚いたか、あらわせますね。 Hope this helps, and talk to you later!

There is NO difference in meaning of these both sentences. They are just two different ways of making the same sentence.

If there is a belief or expectation or understanding that is confounded or contradicted then you would prefer to use 'came as a surprise'. The surprise could then be unwelcome or a shock. On the other hand, in circumstances where the element of surprise is milder, 'It was a surprise' 'It was a total surprise', 'It was a surprising discovery' ... maybe the first form is slightly positive and the second is negative, but not necessarily!

Sorry, meant to say "It was a surprise", not "I was surprise" ... although, "I was surprised" is a good alternative to either of these phrases.

That's a good question. They are totally different, but the difference may be a bit difficult to explain. First of all, "it came as a surprise" is almost always used like this: "it came as a surprise to learn...". It tends to be used when talking about something in the past in a somewhat thoughtful manner. Both phrases could be used interchangeably when talking about the past in a kind of narrative way, but "I was surprised" can be used in a much wider variety of situations and contexts. For example to describe states of physical surprise like if someone threw you a surprise birthday party.