I also just recently got the Optimus G. I think it's a great phone hardware wise, and there's no lag whatsoever, but on the software side it's a bit lacking for me. I am coming from a One V, and I personally prefer Sense 4.0 to LG's UI. The Optimus UI feels much less cohesive than Sense, and it in general seems more like a work in progress. I've also run into a number of minor issues, such as an intermittent delayed response with touch feedback on the screen. And, on a very nit-picky note, I wish the auto-brightness was smarter. I'm constantly going in and out of buildings during the day and it's been getting very frustrating that the screen doesn't keep up with the changing environments as well as the One V's did. Also, the email app is mediocre compared to HTC's, which is a problem for me since I use four different Exchange emails, and there is a surprising dearth of good email apps in the Play Store.
For these reasons, I'm considering exchanging it for an EVO 4G LTE. It's definitely LG's best phone yet, but I'm disappointed in the software (and I have no desire to root).