Every tool I've tried to buy there has broken under normal wear in a ridiculously short period of time. For example, the pry bar that snapped in less than a day. Replaced, and the replacement snapped in less than a day.
Basically, you pay for a 'throw away' tool at Harbor Freight, and then you go buy the real tool from somewhere else. Might as well go somewhere else first.
As for your specific question, there's a reason the slang for circular saws is "Skillsaw". Skill makes a fantastic tool (The Craftsman worm-drive saw is a re-badged Skill).
As for what you need to know, there's two basic designs for circular saw. Direct drive and worm-drive. In a direct drive, the blade is, shockingly enough, directly connected to the motor. The blade is on one side, and you can see the motor directly hanging off the other side. With a worm drive saw, the motor is 90 degrees from the saw blade.
Worm drive saws are more powerful, much less likely to bind and narrower, making them easier to fit in small places. These features are the reasons why pros all use worm drive saws. The primary thing non-pros dislike about worm drive saws is they kick when you start them - right as the saw starts up, it will jerk counterclockwise. Once you're used to it it isn't a big deal, but it is surprising if you've never used one. As for which manufacturer, I frankly haven't heard anyone complain about any of the major tool brands. I stick with Skill, but that's mostly because that's what I've always used.
Direct drive saws are usually lighter and cheaper, which has made them popular among homeowners and others that don't have a ton of lumber to cut. They also don't have the jerk on start. The down side is they are much less powerful and more likely to bind.
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