Ha. I mean it was fine. I totally get the bus terminal vibe! I was fortunate enough not to have to check in or check a bag. The signage was terrible, the windows dirty, and it definitely was a bit more beat up than some others, but it nothing I wasn't already expecting in Mexico. And looks aren't everything, I'll be discussing cockroaches in the new and modern Da Nang airport restaurants...
IMO Viva Aerobus isn’t a bad airline, understanding the cons and pros of flying on a budget airline like spirit or frontier. So you get what you pay for, the goal is to get you from point A to point B. Also viva and volaris have more nonstop flights between many destinations which is imo more convenient than the hub operation model of Aeromexico in Mexico City’s airport. In addition, most of the flights in Mexico are no more than 2:30hr long so is perfectly bearable. For longer flights I would definitely consider paying more and fly with aeromexico.