I've been using Opera GX for a number of months now, and I've been very happy with it. The features are wonderful, and it's very easy to use. One of the things that does trip me up slightly is the lack of a "restore previous session" option. Every time I restart my PC (which happens with relative frequency) I lose the tabs that I had accrued over the past week or two. In addition, sometimes updating Opera GX closes out my tabs and I have to search through my history for the ones I was using.
Most other browsers have a "restore previous session" feature, and I feel that this is the last thing that Opera GX needs in order for it to be a heavy contender for best browser. Would love to see this realized soon!