I found a tourism page that suggested one might mistakenly think of it as a Mediterranean town!
It amuses me that people refer to the Devon/Cornwall south coast as the "English Riviera." Ummm...not to be taken literally. That said, the weather in the southwest is as nice as it gets for England, summers can be sunny and mild (but often unpredictable), quaint coastal villages, great for hiking, wilderness, sailing. Plymouth has a nice ocean front and ready access to all of the above. It's not a particularly beautiful or cosmopolitan city, but it has its charms.
Plymouth Uni: Technology and Sciences are its strongest areas, there's a good research culture and support. Probably not so much in other areas like the humanities. The first thing people will probably mention is that it's a new university. Despite common wisdom, this will not necessarily tell you much about the teaching load and research facilities / support (I'm speaking about new universities generally now): you need to get specific first hand information.