Don't visit on a Saturday, as everything is closed. As someone interested in the issues Masdar is looking to address I was disappointed that there is no visitors centre, and no displays explaining the concept.
There is however an enormous car park (2 actually) and a large diesel powered generator welcomes you if you walk in from the airport (about 2.5km, possible in winter, hot in summer, but you have to walk on the road). Given Abu Dhabi now has a bike-sharing scheme an idea would be to extend it to Masdar.
The place is worth a visit if you are interested in architecture, town planning etc. As others say it is a ghost town. There is a shopping mall (which must be struggling to cover its costs) and a nice park (if temperatures allow), together with a university and other public buildings. The downloadable self-guided tour helps add some context, and the Siemens building has a small display in their foyer. It is however somewhat crazy that that this is Lonely Planet's top sight in Abu Dhabi.

Masdar City is a futuristic area of Abu Dhabi that emphasizes sustainability. We were able to ride in a driverless car.

I really liked it but the area i stayed in was a smal house it smelled but I fixed it it is very enjoyable