The Powerline trail section just after you cross Novelty Hill road is flooded for 11 months out of the year. I believe it's officially a pond now. Use the Redmond Ridge Trail system or Novelty Hill road to avoid this section.
The Puget Power Powerline Trail is mainly singletrack, but there are sections of doubletrack access road and one road section to take you around a couple farms that restrict access to the powerlines.
There are two main climbs to keep your heart rate up. The first is the section from the Sammamish River trail up to Education hill. The first section has a nice set of 7-8 "steps-ups" that will challenge your skills. Power up the hill to Hwy 202, cross through the cross-walk and continue climbing the rest of the hill. This is followed by several sections of wide doubletrack descents with loose gravel in several sections. The second big climb comes after the paved section. Once you come off the road and rejoin the singletrack, choose between the less technical doubletrack climb or the singletrack that is covered in loose gravel, large rocks and typical run-off ruts.
After passing the Redmond Watershed, follow the power line doubletrack trail for another mile to Novelty Hill, where there is a gravel parking lot. A lot of people either park here or at the South entrance to the Redmond Watershed to ride down the powerline trail and then back up for a good out-n-back.