The Dominican people
Thats what you dont want to miss.
I am not a professional when it comes to the DR...but I know from travelling there that you dont want to miss getting out of the resort, and into the villages...meeting the great people of the country, and seeing life through another set of eyes.
There are plenty of ways to get about...and if you get a good taxi driver, and use them everyday...you will get better service, along with some unexpected extra's too..(we had the chance to see where he lived, and meet his family).
I would not though reccomend renting a vehicle...and this will be self explained once you are there. There are many ways to get about without having to do this.
I hope you have a safe and wonderful trip to one of the most beautiful places on earth...both the country-side,and the people.
Cheers
Jimmy