You asked for criticism, so I'll give it: this is a pretty bad rule by itself, and it doesn't seem to be a good basis to build off a cinematic game.
The pretty bad should be kind of obvious, but I'll state three of them:
1) a) It's wildly unbalancing compared to so many things which will probably be the same: it makes rolling for 20's versus high AC opponents not only a good strategy, but quite likely the best one, such that not only will players occasionally do this, but mooks will probably do this all the time. b) It's wildly unbalancing compared to tons of feats: would you rather take your +10 attack? or 10 attacks at -4 from doing a -5/+10 power attack. Let alone the questions of: take one +5 attack with +3d6 sneak damage, or 5 +1 attacks with +3d6 sneak attack on each one.
2) You've thrown this wild imbalance at melee, and done nothing to magic.
3) You've most likely made the game more complicated, not less, and less cinematic, not more. You've increased turn paralysis, increased dramatically, the number of rolls and math involved in a combat action. (I take 10 attacks with my 2d6 greatsword = ugh). All of this, for a system which adds little narrative benefit, other than that players can now take out mooks faster (a decent goal, but the costs are too high).
This isn't to say that your playtest might not be fun: there have certainly been worse systems, and worse house rules, and a good GM and players can overrule that: I'd just caution you strongly from taking this as a bedrock.
I completely sympathize with the "cinematic d20" goal: even in story-oriented games that I play, the game just comes crashing to a halt at the occasional combat, and we break out a tactical wargame for a while.
Here are three areas that I think need to be addressed, or dodged, to create a cinematic (or narrative, not the same thing, but the goals often coincide) game.
1) You need to reduce the cruft. I'm sure that there are some groups out there, who are so well-oiled, or using so much computer aid, that combat just burns: people know who's coming up in the initiative order, and are rolling their attacks and damage before the GM even says their name. I've found this is very very rarely the case: in most cases, combat drags, people take about 30 seconds to a minute to fully adjucate their actions, and after that, who wants to waste more time with good descriptions: so first is that you need to simplify the number of rolls, the number of charts, the number of modifiers: the rolls needs to be fewer and simpler.
[Mutants and Masterminds does just this: there are less modifiers, less rolls, and its easier to know exactly what your roll is, since the d20 is the only die, and skills don't fluctuate often.]
2) You need to simplify the options. In a cinematic or narrative game, the number of viable options goes up (swinging from chandeliers), but yet, you want the adjucation responsibility to go down (no looking up the swinging from chandeliers page). So you need more generic systems: Feng Shui has an elegant system: as long as it's doesn't make a huge difference with regards to what actually happens, it doesn't affect the difficulty. This may not be satisfying for all, but you want to strip things down. Stripping down the actions to at least the half/full dynamic is good: going to just one action a round with free actions is even better.
Magic is a particular problem: the AU spell system is nice, but would be absolutely horrid for any cinematic game: the amount of flexibility involved would lead to horrible turn paralysis.
3) Finally, you want something which encourages various cinematic feels: you want stunts. You want mooks who go down quick (hit points = no no!). You want the ability for villains and heroes to give monologues during combat. You want some sort of metasystem (Hero Points). You want a system which might drag more narrative control back to the players. And, yet, you want all of these to be simple. (FATE,
www.faterpg.com , is a really interesting narrative-based system (non-d20), which might give you a huge amount of ideas: the Aspects and Fate Points are particularly ingenious)
You actually don't necessarily want all of these being mandatory, but you want a game system which can express all of these ideas.
4) You want a pick up and play game. All of the above things have to be factored as: I should be able to go to a con, teach people the game in a few minutes, and go from there. M&M is okay as far as this, Feng Shui is great (people who haven't rollplayed before can generally create a Feng Shui character in a few minutes). Fudge and FATE also are pick up and play. D20 is generally kind of pick up and play: it's easy to explain how to handle non-combat stuff, and even occasionally spells, but combat just tends to drag.
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