So I've been playing on ICCup and 1v1 comp, and it's significantly more challenging than 2v6 comp without the launcher/patch. I can handle comp zerg alright, but I got absolutely destroyed by toss. Haven't tried Terran yet but I'm sure the flawless micromanagement of nuclear strikes, lockdowns, and yamato guns will be obnoxious at best.
I think my real downfall is limited resources. All the popular ICCup maps seem to be limited resource, and I always feel uneasy expanding without proper defenses. A decent base with no defenses costs 1100 minerals, so I'm not really fond of losing them, especially when resources are so scarce.