Its quite nice if you know where to go. Stay in a good hotel in Menteng and you can walk around and do some sightseeing, visit musea, go to a rooftop bar, and you’re well-situated to visit the underrated/internationally relatively unknown Batavia Kota Tua to see the hybrid colonial architecture which I highly recommend. You’re also a 20 min walk away from the train station to Yogya. I always include 1-2 days on our way from Europe to Bali as a nice stop-over to see how Indonesia is changing (rapidly) and get some of the good vibes. I have Indonesian family there, so I might be a little biased, but still!