TCD has the beauty of Oxbridge, as well as lots of history and prestige. Also, you can get a degree from there which is considered of equivalent standing to an Oxbridge degree, in the event that you wished to transfer between these universities during your degree. I think there is more to it than this, but it is a sign that a degree from TCD is of high quality.
Edit: Trinity College Dublin is a sister college to St John's College, Cambridge and Oriel College, Oxford, and by incorporation, a graduate of Dublin, Oxford or Cambridge can be conferred the equivalent degree at either of the other two without further examination. [Source: Wikipedia]