I've been riding on Mallard/Clarks Creek Greenway for several months now. I'm new to cycling and figured that this would be a good learning point before dealing with traffic on the open road. Plus it's one of the only Greenways in this area that is longer than 2 miles one way.
The paved section is around 10miles (out and back) so you can get a decent "newbie" ride. I like and don't like how it winds behind housing developments. It's nice to see what the Jones' are up to but also kind of creepy thinking that you may be watched. The route is a good workout with some small, slight climbs and turns. Parts of it is uphill a little bit (mostly heading back from Saxonbury way). There is a lot of activity during the warmer days. Plenty of dog walkers and other fellow bikers.
Parking at the Elementary School can be limited, especially if going around 2 o'clock and the uphill climb is brutal when you are returning to your car. There is also parking along Saxonbury way which is very accessible and if you're eager for more, then you can ride throughout the neighborhood too.
The trail is decently maintained but I think that may have to do with the budget cuts in Charlotte. You will definitely find better maintained Greenways in the counties north of Charlotte (i.e. Davidson and Cabarrus). The main issue with this is dodging sticks and debris after a storm the night before and also navigating across the bridges. I'm afraid of losing a tire over some of them with their gnarly, knotty wood. It would be nice if they had water fountains and Doggie Depots along the greenway but I may just be spoiled from Cabarrus County.
You can easily make this a 12miler by adding the University Research trail and the Kirk Farm Fields trail. I will say that if you have a Road bike then it may be an uncomfortable and unstable ride through the research park as it's loose gravel/rock. However, if you are on a Hybrid bike or MB then you will do just fine. I particularly love the Research trail route for the scenery along the creek. It reminds me of a winding forrest trail in the mountains.