There are differences, of course. Sam Beckett mind-traveled into the heads of real people who played various roles in crucial events in the past. Lucy, Wyatt, and Rufus travel physically to the past. And so far, as of the first five episodes, Timeless is dealing with bigger, often world-shattering, or at least America-determinative events than did Quantum Leap, where Beckett often dealt with more minor, even off-the-radar situations in history.
But the episodic tempo of the two series is similar, with the stories in each episode having no connection to the others, other than our time-travelers being the same, and, in the case of Timeless, a central story with an apparently bad guy time-traveler, Flynn, in the thick of it from the very beginning.
You might think that a captivating central story to tie the episodes together is a plus, and it can be, but it can also be a hindrance to the series, because its existence requires the series to decide how much information to dole out this underling story in each episode. Quantum Leap suffered from no such problem. Neither does Frequency, another time travel series on the air this season, which operates on a very different scale than Timeless. But other science fiction series, such as Lost and Westworld, did and do. I enjoyed Lost - at least until the very very last episode, which was atrocious - and think Westworld is one of the best series on television now, but critics have expressed frustration with its low ratio of answers to questions, and viewers can be lost in those kinds of gambles.
So far, Timeless has been doing a good job in threading this needle. It will be fun to see how it fares in the weeks ahead.
See also Timeless 1.1: Threading the Needle ... Timeless 1.2: Small Change, Big Payoffs ... Timeless 1.3: Judith Campbell ... Timeless 1.4: Skyfall and Weapon of Choice
more time travel in the 20th century