> it crashes all the time, features are so amateurish (vs teamcity especially) that we're struggling just to do basic things.

Do you have an on-prem instance? What sort of features does teamcity have that are not there in Gitlab CI?

Teams in my org are currently switching from Gerrit/Jenkins combos to Gitlab and I have been pretty pleased so far. I do wish there was a nicer way to experiment with different CI configurations from within the browser to prevent a bunch of pointless commits messing with your config YAML; but, otherwise I have been pretty happy with the flexibility.