Brnn, Bucharest and Oradea or Iasi would not be at the top of my list of places to see in Romania. Do you have special interests that are focusing your attention on those three?
I only did quick trips to Oradea and Iasi. Oradea has some striking Art Nouveau architecture, but I'm not sure what it has in the way of go-inside tourist sights. (Try checking TripAdvisor.) Iasi is a pleasant university city, but I didn't find the distinctive architecture seen in Oradea. Unfortunately, I was running late and didn't have a chance to check out the botanical garden.
Places I found much more visually arresting included: Timisoara (also historically important as the birthplace of the revolution), Cluj-Napoca, Sibiu, Brasov, Sighisoara. In addition to the fascinating Maramures (wooden churches, carved gateposts, Merry Cemetery), the Bucovina area is very interesting (painted monasteries). The Retro Hostel in Cluj-Napoca organizes 2-day van trips to Maramures (plus many other excursions in Romania), which I highly recommend. You don't have to stay at the hostel to take the trips.