http://www.rpg.net/news+reviews/reviews/rev_6743.html
There is my review of SAS, and RPG.net has several more as well... just search the review database. Sure, all the reviews are for the tri-stat version, but the 2 games are extremely similar, so all the info about "what's in SAS, and is it any good" is pretty much universal.
That said, I don't own the d20 version and have only glanced at it in the store and heard comments by people on the forums (same forum on GoO's site serves both versions...) It seems to have more editting mistakes than the Tri-stat version because they simply took the tri-stat manuscript and changed the rules parts to d20. Several times, tri-stat numbers and references seemed to have slipped by them... There is a d20 - tri-stat conversion section in the appendix, though, so it is not impossible to figure out on the few occasions it happens.
The game has multiple character classes, but also the option to use one 1 of them if that is prefered (the somewhat generic "Adventurer".) There are no Feats, at least they are not called Feats, but the powers duplicate many of them. Combat Techniques is a power that allows 1 Technique/ level, and many of the abilities match combat Feats. Henchmen and Sidekick replace Leadership. Highly Skilled is a power that duplicates all of the Skill Focus-type Feats, while Heightened Senses, Attack Combat Mastery, Defense Combat Mastery, Enhanced Stat, Massive Damage, Special Defense, Special Movement, Tough, etc also replicate many of the abilities of Feats. The few feats not covered by these powers/ abilities can easily be added with the "Feats" power that GoO posted earlier in this thread.
SAS d20 was made to conform more closely to SAS than D&D. That may bother some people, but the end result means that the supplements will include a bare minimum of wasted space. Instead of requiring a complete seperate page of stats for the d20 version of each character, item, etc (which would make fully half the book useless to players of each game!), only a small 3-line box with stats, attack and defense info, etc) needs to be altered for each character. The powers, skills, and defects boxes, which take up 90% of each character, are usable by players of both versions. Had they not done it this way, there is no way I'd buy a half-useless supplement, and I'm sure the d20 players would feel the same way. If SAS (both versions) wants to sell its dual-statted Rogue's Gallery-type books (which are always the most popular kind of superhero supplement!), it HAD to maintain maximum compatability between the 2 systems or else it would just not work.
I think that those gamers who are willing to give it a try and keep an open mind will be quite pleased with the results.