This drama is a good choice for those days when you don't want anything overly dramatic.

The plot is not dynamic. But this is not necessarily a bad thing; as it perfectly sets the background for the story to unfold.
It had the time and space to provide detailed insights on how start-ups are established and the difficulties they might face.
From that perspective, I found this drama to be very informative. You actually get to learn something from it.

There was an attempt to add a touch of mystery to the plot to make it more engaging, I guess. But ultimately, I felt like the writers desisted from it. (Much to my disappointment)

As for the characters, I wasn't focused on the main leads and their chemsitry. (They were just ok, if you ask)
The relationship between Han Ji Pyung and the grandmother is the one that gave me the warmest feelings.
Han Ji Pyung himself, is a very charming and charismatic character. Probably, my favorite one.
The other characters are all likable, and not very k-drama typical.

All in all, "Start-up" is a drama worth-seeing if only for its charachters and unusual topic.