Sussex ranked 11th, 14th and 19th in UK league tables this year, so it is cearly a very reputable institution.
For those who aren't familiar with the UK league table system, the top 30 is usually dominated by Russell Group institutions. Many of these are older universities that have had many years to develop and reinforce their reputation as national leaders - examples include Nottingham, Bristol, Manchester etc.
Sussex however was established in the 1960s, and is only 50 years old. I would put it alongside places like UEA and Lancaster - very good universities that have not been around long enough to establish themselves globally to the level that older institutions have.
When you consider the size of Sussex, I think it's doing pretty well for itself. It has a mere 12,000 students, and still ranks alongside places that have 3 times as many
In short, it's definately a good university that i'm sure will develop well into the future