Haven't played, but saying it's purely a roll-under system is not entirely true. It uses roll-under, but it has a quality-of-success mechanic, and doubles are criticals. Other than that, it's a fairly basic percentile system. Also, one thing to note for people who dislike point-buy systems. Not only is it a point-buy system, player characters start out with 1000 points to begin with, and a lot of things cost 5 or less points, in addition to some freebies which are handed out. Twinking is lessened if only because a number of the points are mandated to be spent in certain areas, though there are still some things which may need to be houseruled, like the prices of starting morphs (morphs cost more if you buy them via CP directly rather than through cash paid for through CP, for example). Having a spreadsheet to add things up is very likely to be a good idea, particularly since the game recommends saving characters to account for characters forking themselves or having backups made. One other thing to note is that the game doesn't come with rules for making your own morphs yet, but there's fan-made rules for that that seem to jibe pretty well with the core material out there, so if you want something different, search for 'em at places like RPG.net or on the EP forums.
That said, the setting material is excellent, and the game doesn't lack for potential antagonists and allied groups, even if you don't go with the assumed default campaign. One thing to note is that there's no adventures currently published, so you'll have to roll your own, at least until the GM's screen comes out, as it comes with an adventure, and likewise, information on specific areas of the setting is usually pretty sparse. You'll see stuff about the general conditions on Mars or in the Oort cloud, but other than occasional mentions of things like the MeatHab, don't expect detailed info.