Untrained skills are very difficult to use. You have to get 4 on a d4-2.
PC's have the Wildcard die (SWD 2015 p.62) so it's 4+ on 1d6-2... NPCs generally cannot do it, lacking the wild die.
While I have not played nor run Savage Worlds, I have sat in on a couple sessions by a GM who loved it... (His car was in the shop, and I agreed to run him to his game and home again)
The swingy is really, really problematic for me. Bennies are supposed to reduce the impact on PCs... but players who have yet to learn to work the bennies system or whose GM is stingy about them, are going to have random nastiness.
One random reduction I've seen is making the standard roll 2d for NPCs and 3d for Wildcards (including PCs). Standard becomes d(Att) + d(Skill) keep high, with wildcards also keeping the d6, but the unskilled becomes simply d(Att)-2.
I've never pulled the trigger on playing SW, but I have a number of setting books for it from bundles...
To list the drawbacks I see, which are why I've not run it myself ...
Minor: Essentially level-based advancement (every advance costs 5 points)
Minor: only 5 levels of ability per ability.
Minor: bennies gain very subjective
Minor: pure point build
Major: super swingy
Major: Up/down/off
Now, one thing I've considered is using the Cortex Plus mechanics (either from Firefly or from Marvel Heroic) with the characters being built using SW, then adding 3 distinctions.
I will say the writing is top-notch, and the design does largely what the designer claims... fast and furious, low bookkeeping, miniatures friendly combat. For me, it doesn't look fun, but my friend Jerry enjoys the hell out of it.... for him, the level-like advancement, the swingyness, and the up/down/off are edges, not flaws.