Is consumer surplus subjective?
Yes it is subjective. But subjective valuations are where demand curves come from (at least for final goods and services). Consumer surplus is simply a measurement of aggregate willingness to pay so it is subjective (like utility) and measured in currency units (unlike utility).  

For example, if a movie ticket is for sale for ten dollars and you'd pay up to 15 dollars to see it then your consumer surplus is five dollars. This valuation is purely subjective. Another consumer could have a different maximum willingness to pay for the ticket. If you thought the movie was going to be less entertaining or had something else fun to do the maximum you'd pay would be lower and so would the consumer surplus. 

One area of this that once confused me is the units. Utility functions typically are discussed as though they were in units of utils but utils cannot be compared across people. However, willingness to pay, which is an implication of the budget constraint and preferences implied  by household utility functions, is measured in currency and can be compared across people. That is, it is sensible to say "you would pay more to see Iron Man IV than I would" but not "you would get more utility from seeing Iron Man IV than I would". 

So it isn't exactly as @Kitsune says, that consumer surplus is utility minus price. Rather, consumer surplus is willingness to pay minus price, which are both in currency units and can be aggregated over and compared across consumers.