That was my first thought as well, but after playing around with it all afternoon, I'd say that I'm "cautiously optimistic". It's quite snappy, and they clearly put a lot of thought into optimizing what it shows and when. It would have been super-helpful when I was first getting started with MMA, and as an experienced user I'm finding myself using it more than I would have expected.

My one gripe thus far is that there isn't as much keyboard control over the prediction interface as I'd like, but that could just be that I haven't found the shortcuts yet.

One thing I quite like about it is that there's a built-in "feedback" feature- any time the "predictive UI bar" is showing, there's a button you can press to send semi-structured feedback about what's currently showing, suggest other things you'd like to appear in similar situations, and so on. I've used it already to suggest a few changes the prediction UI for ListPlot.