Time Travel DLC sends you into stone age after the first 3 puzzles, where you explore usage of new elements for remaining 47 puzzles in Stone Age theme. Which may be a part of professor's sick imagination.
So yea, it's pretty nice. It introduces few character-like elements, quite unusual thing for Crazy Machines series, and a few others Stone Age elements. Though, having only one theme for majority of playtime may sound somewhat tired, music isn't much hot either.
The puzzles don't disappoint. They start quite easy when introducing new elements and then get as complicated as in the original CM2. They however lack the instructions, you have to press "i" icon to get some. They also rarely have bonus objectives.
It's still was quite addictive to solve all these puzzles, with some slight placing requirements. There are some puzzles where you will have to tweak around to make physics of unrelated object work for you, but there is no outright broken puzzles like in Back to Shop. Also, protip: ice cube isn't perfect cube.
So yes, recommended to those who want more of CM2.