The opera in Budapest definitely belongs to one of the most magnificent buildings in Budapest. Especially inside, the opera is very impressive. Until the spring of 2020, the opera will be restored. Until the reopening the concerts take place in the Elker Theater.
A visit to the opera for a tour is currently still possible. However, depending on the work currently in progress, not all rooms are accessible.
I just attended the tour, unfortunately, the main hall was not accessible and the mini concert you get after the tour took place in the stairwell. All in all, I still think it was worth it. The magnificent staircase were great and the singing was really good.
If you just check off Budapest from your bucket list and do not know if you come back so quickly, then you should go for a visit of the opera. If you want to go back to Budapest in the next few years anyway, I would rather wait for the completion of the restoration and postpone the tour to the next time.
The tour through the rooms takes about 30min. After that you can listen to a mini concert. Current information on tour prices, tour languages and times can be found on the page of the opera: