First and foremost, I didn't like the gates after you purchase the ticket.

The ticketing is accepting only coins, it was troublesome to get money change into smaller denominations to fit into the ticketing machine.

With the baby buggy, it is not allowed to have the baby sitting or sleeping in it. You got to hold your baby and close the baby buggy! :( This is annoying cos it is a system that is not delivering convenience. The problem with Budapest metro is it is with steps going underground at most stations. So it means you got to lift the baby buggy together with the baby in the buggy and walk up or walk down the steps. If you baby is 8.8kg, it means you will have to lift 8.8+6.1kg, total 14.9kg

It is almost the same noise level - NOISY. 

The doors do not open by itself automatically. 

You got to pull to the side, to open the door manually!