I've taken the Metrolink for two trips from Irvine up to LA, and for both, the trains left on time which I appreciate.
When I went this month (Jan 2020), there was also ample seating, so you don't ever have to worry about finding seats. Some seats (could only find one) have power sources next to them.
Some of the mezzanine levels also have tables if you need to do work/eat, which was great for me.
The trains are mildly shaky, but not to the point that it's distracting, and I find them quiet enough.
My favorite part about taking the Metrolink is free transfers to LA's Metro subways and buses. At the stations, you just scan the QR code of your Metrolink ticket (I bought my tickets on the app) to enter the platform. For buses, you just show your QR code to the driver. I thought it was very convenient and definitely a good incentive to take the LA Metro.