Some more positives include quick and easy set-up, with the press of a button I'm recording and shadowplay can always be running the the background (like it was designed to) and if you have 'shadow' mode on it even records up to 20 minutes of the past for you. Other than those tho I'd say it's pretty amazing! Shadowplay also lacks a lot of advanced options and only goes up so high in resolution, 1080 is supported tho, which is more than enough for most people. That won't effect most people but for people like me that do stream it's a little annoying having to deal with exports and youtube's slow downloads. Shadowplay also can't record AND stream at the same time, it's one or the other.

Shadow Play records in a varied framerate which means without using something like handbrake to re-encode at a constant frame rate the video will most likely appear broken in your editor (this was mostly fixed with premiere but I don't know about others). This isn't actually that big of a deal either, most recording software doesn't have more than 1 channel anyways so something like Audacity is a must regardless. There's also the audio channels, it only records 1. I personally can't see the difference between shadowplay videos and downsized videos but it's argued just the same. First off the compression is already lossy, this doesn't matter much but some people still argue the point. I'm NOT joking, I can record anything and barely lose a frame a minute. ShadowPlay has a HUGE perk in my opinion, your performance will have no noticeable impact while recording.

Nvidia shadowplay guide