There were quite a few time travel shows that popped up 2-3 years ago. I've written about DC's Legends of Tomorrow on the CW (which has improved greatly since a weak season 1) and Netflix's Travelers. Frequency on the CW was pretty good, but only lasted one season. And on NBC, we have Timeless.
The world of Timeless: Time travel has been invented with the backing of deep pockets from a shadowy organization called Rittenhouse. They want to use the time ship to entrench their own positions and mold society to their ideals, which needless to say aren't progressive or friendly to anyone outside their group. A small team of uncorrupted government agents and civilians use a prototype time ship to thwart those schemes.
Like most shows based on time travel, you can't think too deeply about the premise of Timeless. The only real restriction is that you can't travel to place where you already exist, and there's ways around that (like recruiting others). The show establishes pretty early that changes made in the past do affect the future, so you have to ignore the fact that it would be incredibly easy to make a mistake that would wipe out your desired result, the development of time travel, or even all life on Earth. So watching Timeless definitely requires you to turn off the bit of your brain that tries to make sense of the whole time travel aspect.
Once you've got that suspension of disbelief going, Timeless is a lot of fun. I like pretty much all the characters, particularly Jiya and Rufus since they're nerds like me. (Younger and smarter and better looking, but then, who on TV isn't?) There's a decent amount of family and interpersonal drama that for the most part doesn't detract from the overall storyline, and in fact usually plays into it. Nice to have writers that make an effort to integrate the emotional drama, not just tossing it in on the side.
But my favorite part of Timeless is the historical characters. Pretty much every week, the crew goes to a different part of history and meets one or more pivotal persons. There's plenty of the usual suspects: the Alamo with Bowie and Crockett, Bonnie and Clyde, the revolutionary war with Benedict Arnold and George Washington, Al Capone and Eliot Ness in Chicago, etc. But some of the best stories are with lesser known characters, like Katherine Johnson at NASA (better known now after Hidden Figures) or blues musician Robert Johnson. Timeless does a fine job of bringing these characters to life, generally with a minimum of deviation from what we know from history. (The Smithsonian does a weekly blog post checking the facts.)
The second season wrapped up recently, with a cliffhanger that shows that the writers are ready to go for season 3. Hopefully NBC lets them keep going, or someone else picks it up.