I also live on the IoW. Been here almost 7yrs. I'm not retired though.
I can tell you the good, the bad and the ugly. The bad is mainly the cost of and reliability of the ferries. Wightlink offer a saver bundle (forget what it's called) if you're planning on travelling back to the North island regularly. Also, its worth knowing that there's a shopper boat from Cowes to Gunwharf which is £10 return and free parking.
Doctors can be hit and miss. My surgery used to be a few doors down from me. That's closed and now I have to drive 20 mins to an alternative. My 91yr old neighbour pays £15 each way in a taxi to get there. I'm yet to find an NHS dentist.
A few of my friends have cancer, sadly. As PP said, you have to travel to Southampton or Portsmouth for treatment. I had to have a back procedure and was sent to Winchester.
A friend told me that the longer you live here, the bigger the island gets. She wasn't wrong! There are so many beautiful places tucked out of the way. When I read the local news, I often have to look on Maps because I've never heard of the place before!
Wherever you decide to buy, make sure it has parking. Parking is the pain in the rear of a lot of us here.
That said, it's a fabulous place to live and I'd never, ever move back. My social circle is huge, I love that my road is like Coronation Street where we all know each other and help each other out (not for everyone, I know). If I pop into town for 10 minutes, it will take an hour because I either bump into someone I know or get chatting to a random. There are theatres, art exhibitions, cinemas, masses of restaurants and cafes, independent brewers, distillers, fantastic farm shops - in fact, the other day, The Guardian listed Newport as one of the happiest places to live.
You'll have a very fulfilling retirement here! There are also masses of volunteering opportunities so you won't be bored.
As an aside, if you're coming over in the next few weeks, beware of traffic issues we currently have due to some road closures. Also the Festival is coming up and that causes mayhem!