Opinions differ wildly on bags, and it really depends on what you expect from the bag and how you want to use it (car camping, backpacking, leave in vehicle, SHTF/BOB, etc.).
My $.02... Kelty makes great stuff for the money and a $30 bag from a reputable company is tough to beat. It sounds like you have reasonable expectations. Basic rule of thumb is add 10F to the bag's rating to get a "real" rating (aka EN comfort rating). As for the insulation, this is a basic synthetic bag, nothing cutting edge, but nothing wrong with it either.
I've said many times that i wish I would've bought a Kelty Cosmic Down 20 for my first bag because they can be had for about $100, are warm (I sleep cold), are down and therefore compressible for backpacking, and down bags typically last longer than synthetic if cared for properly. The new Cosmics use water resistant down like last year's "ignite" version.