After using these gates for a month and a half, my feeling is that they're generally working well, but there is room for improvement, but nothing that seems like a fatal flaw so far.
In general, the gates aren't a huge impediment. During the morning rush, the longest wait I've had has been about 30 seconds, which isn't too bad. In the evening, there's never a wait as the people arrive over time rather than all at once like when a train arrives. Staff is also available at each gate to help keep things moving. The waiting area itself seems less crowded and has far fewer people just hanging out.
Every day multiple gates are broken and are either "closed", not reading CR codes, NFC not working, or something similar. The sheer number of other gates mitigates this, so it's not a massive issue. For those used to Charlie Card fare gates, the ones at North Station seem abysmally slow. Reading CR codes from the mTicket app also feels much slower than similar things elsewhere. There's also no tap and go or capability for multiple people to tap and exit in one gate open/close cycle. Another meh is that it can be hard to get the T staff's attention when they're busy on the phone or chatting up other T staff & transit police. This seems to be more of an issue during less busy times.
This happens to some degree on the subway as well, but seems MUCH, MUCH worse here. Every instance I've seen of someone looking to ENTER the gated area during the morning rush of people trying to leave has required T Staff to yell at people to let them in.