I've been swapping things from a d20 to a "Dice Pool", the core mechanic change rippled through the system like a tsunami, but also caused the rift between this and traditional D&D to widen greatly. My reasons for doing this was simple...There's simply no story that can be told with a single die roll, it really boils to to success or failure, and not much else. Yeah sure, "Nat 20" is an epic success, and "Nat 1" is a horrible failure, but it's too much.
My favorite example in this area is the 20 Str Barbarian attempts to open a stuck door, let's say the party is 10th level, so the Str Check for the Barbarian is a +10, and the door is really stuck, DC 15. The Barbarian comes at it, and rolls a 3, for a result on the Str Check of 13...Fail. The next vocal member of the party is the Wizard, with a Str of 8, for a +4 on his Str Check. He walks up to the door and rolls a 13, for a result of 17...and the door is open.
Now thinking in terms of a Dice Pool, a simple pool is a base dice, with an extra dice added per Rank of the given skill. So, in this example, I'll just use a d10 as the base dice, and a d6 per Rank. To avoid "negative" dice we'll assume the Wizards base Str is Rank 0, and that would put the Barbarian at Rank 6 (assuming eack +1 grants a rank). Since a DC 15 is fairly easy in game terms, and anyone would pretty much succeed about 30% of the time, let's assign the DC of the door to a 8, which is what the Wizard would need to open the door (and 8, 9 or 10 on the d10 would open it, so 3 in 10 or 30%). However the Barbarian with a Rank 6 Str, now rolls a d10+6d6 now only by rolling a "1" on every dice does this guy fail...nearly 2 in a million chance of this happening.
Maybe rather than the Barbarian being defined as Rank 6 Str, they might be Rank 3 At 20 Str, but even that would give them a distinct advantage over the Wizard, d10+3d6, would result in a shaped curve averaging on 15, and to fail on a DC 8 check would very rare, though the scenario of the Wizard beating the Barbarian is still possible, it would be very rare.
That's about the simplest example of a dice pool, other systems like "The One Ring" add much more story telling aspect to the dice rolls. In this system the base dice is a d12, sides are numbered 1 to 10, then there's an Eye Rune and a Gandelf Rune. The Eye when rolled essentially not only is a "0" for the base dice, but often denotes a very bad result occurred. The Gandelf Rune on the hand counts as an automatic success. To go with is special d12, the players roll a d6 per Rank, with a "6" also denoting a "Special Success".
So, if a player has 3 Ranks in a task, they roll the d12+3d6, against a given DC of a task, often around 14. But, say the d12 was an "Eye", and the d6's were a 1, 2 and 6. Even though the total is only 9, the 6 that was rolled denotes a "special success", along with the Eye being something tragic. This allows an interesting story telling opportunity..."While struggling picking the lock Ravi (the Thief) was forced the lock too hard and his pick actually broke off in the lock, then while fishing out the piece he heard a click as the lock popped open and the broken piece fell to the ground."
A long time time ago I decided that the d% were worthless, as if normally came down to a d10, and if rolled the one edge number then the 2nd dice mattered. The d20 really seems to be that same way, at least as far as 4E goes. It just seems that all characters in 4E begin at +4 to +5 now on their main stat, and then you factor in the weapon and it goes up to a +8 to hit at 1st level. Then the monsters essentially scale to factor in this max'd bonus, so your forced to MinMax or die. Worse yet, you get artificial bonuses every other level and assumed magical weapon bumps every 5 levels, but none of this matters either, because the monsters all have increased Def as well, so it basically comes down to consistently rolling above a 10 in battle (especially on encounter powers or daily powers). At least in the "Old School" editions, every bonus to hit really mattered, and AC wasn't so much a factor of a creatures level, so your bonuses seemed to make a big difference...In 4E and Pathfinder to a lesser degree, the attack bonuses are simply expected to survive, and if your not MinMax'd then your not going to make it.
This is the reason for me reworking the mechanics of the system to move away from a d20, and move toward a Dice Pool. It turns an Attack Roll into a "fortune telling" event, there's good and bad in most rolls, the overall success if easily determined by simple calculation, but there's often more of story to the result than simply a success or failure result.