If you are traveling to Houston for the first time and have never been to the Johnson Space Center, then you should pay to a visit to Space Center Houston. Just keep in mind that there will be a lot of limitations due to COVID-19, but there are still some activities that can be done during your visit. Also, if you are visiting several touristic attractions during your stay in Houston, please make sure that you secure the City Pass, since it will be less expensive if you visit more than one attraction.
As soon as we arrived to the location (30 minutes away from Downtown Houston), we were able to move forward easily through the line, and then check in with our ticket. We arrived around noon, and it was extremely crowded. Even though guests were wearing masks, there was no social distancing in this place. A few attractions and/or movies were accessible during our visit, but most of it includes a lot of walking around through some exhibits. In addition, you have to download an app on site (that keeps crashing every single few minutes) to be able to secure one of two tram rides in the center. I would highly recommend that you spend more than three hours if you really want to enjoy both tram rides and exhibits, since you can only secure one tram ride at a time.
Living in Orlando, FL for so many years, Kennedy Space Center has been one of the main attractions that we visited and enjoyed over the years. The experience in Johnson Space Center allowed us to reconcile many aspects of NASA and what the entire mission of this place is for space exploration, but was not truly impressed with this location when comparing it to Kennedy Space Center. I might try to come back after COVID-19 and things are more accessible.