this build is designed to keep you at a competitive pace with the many ap mages youll be facing mid. lots of mana regen and magic resist will keep you spamming your q and give you extra tankiness allowing you to harass better while also having a defensive edge in any fights you pick. yes there are no attack speed boosts besides triforce but you should be able to list hit well enough without them and ezreals passive takes care of that during fights. with these runes and masteries you shouldnt be running out of mana unless you get into a long extended period of overusing your q/e.

the 11 points in offensive masteries are all about cooldown reduc and armor pen to both spam q and make your attacks more effective. 19 points in utility to increase your regen rates (by however small an amount) increase your xp gain toeither stay on par with opponents or significantly outlevel them if they need to back more than you do, extra mana regen for more q spam, increased buff duration, and movespeed to help you dodge with a final 3 points in more cd reduc.

mystic shot mystic shot mystic shot. the cooldown on this ability makes it 10 times more useful than eflux and it scales off of both your ad and ap now, with (as always) a 1:1 ad scale ratio. arcane shift is the next skill to focus because the mobility it grants as well as some extra damage (it is actually a great ks skill ;D) make it worth the long cooldown that it has. naturally you want to level up your ult at 6, 11, and 16 but be aware - ezreals ult loses power as it passes through enemies (minions, jungle, champions) making long distance shots often too weak to kill an enemy if it hits to many creeps. with a relatively low cooldown for such a great ult you should not be discouraged about using it because there will be many chances to do so - you dont need literally every single shot to count. your ult is also a great way to start off a teamfight - if you can hit 4 or 5 of your opponents with it at close range the psychological effect can be significant: your team will be encouraged to take them down and they might start to retreat when suddenly most or all of their team is 20-33% short of hp. lastly your w is slow, shorter ranged, and not particularly powerful until lategame (even then it is mediocre) and the most useful thing about it is slowing down an enemys attack speed or speeding up an allys. this is great for ad carries who are taking down turrets or if you are in a 1v1 with a twitch it can bring the balance into your favor.

marks - apen if you do not take these o do not know why you should then just stop playing ezreal right now
seals - mana regen spam that q
glyphs - magic resist if youre gonna be fighting an ap carry in mid who does a lot of dmg (leblanc, annie, brand, malz) you might want the mres to help keep you in lane longer. you can also choose to go for cd reduc (i prefer flat because it is more useful early game if you can spam you q like crazy b/c early game your q rapes most ap mid champs) to help you spam q more.
quints - i generally go flat hp b/c ez is so squishy, with dorans blade your level 1 hp will be 608 which can be a pretty nice advantage to have. naturally if you dont need more hp b/c youre too pro i would go either apen or cd reduc for quints.

start off dorans - more hp, more dmg, lifesteal helps you regen
boots - mobility is important for ez b/c he is squishy, dodging skillshots is very useful
bf sword - this will help you farm and boost your q dmg, i usually stay in lane until i have 2k gold and get boots and bf at the same time but if you get beat early, id go boots first (also you might only have enough money for them :P)
sheen - multiplies your q dmg, when you use q it will apply to that q so basically sheen + q spam = win imo, also gives you some extra mana and ap
merc treads - i usually get mercs b/c of the mres (again, good for facing ap carries) and the enhanced movement but you can also go ionian boots for the cd reduc. if you get all the cd reduc masteries and the cd reduc glyphs, ionian boots will keep your q flowing nonstop.
last whisper - gives good ad as well as the ever important apen
building better stuff - the last four items are more of a toss up in order, depending on what you need. need lifesteal? go bloodthirster. need survivability? go banshees. need all around pwnage? go triforce. i usually save hextech for last tho.

ignite - pro skill that wins game with that extra dmg, dot, and heal suppress. great feeling if you kill someone after they retreat with ignite.

flash - mobility and dodging are important on squishy characters like ez and double flash (flash+arcane shift) is a great way to speed across the jungle or elude the other team if its a 5v1.

b/c ez is a cc desert exhaust can also be useful, especially when combined with ignite.

cleanse seems like a good idea but ive never used it on ez.

this build is designed to be more durable against ap carries in mid and to suppress your lane with q spam while getting through enemy armor with apen. it is also important to remember that this is not the hard and fast way to play ezreal every time you play him and that even in the situation this build is designed for it is sometimes necessary to switch up the build order. the most important trait a good player can have imo? flexibilty. hope you guys agree with some of it :P peace.