A lot of people believe that Akali became in-viable as a champ when the Gunblade nerf came around but that is far from the case. When either solo or duo lane top when she hits lv6 all it takes is the patience to reach 3 stacks of your ultimate to burst most champs down instantly from full hp. As well as this, Akali is without a doubt one of the best ganking champions in the game, able to do heavy amounts of damage and able to ultimate towards them from quite a large range giving no obvious clues you are there unless wards have been placed.
In teamfights her job is to take out the squishier damaging champions such as the range ad's and other assassins which is usually incredibly easy as the tankier champs will be in the midst of the teamfight itself.
Although you may think clean-up is kill stealing, Akali can easily solo 4 champs of lower hp on her own as her ultimate gains stacks every kill. I often find it difficult to go through a game as Akali and not get a triple or quadra kill somewhere down the line but a good team should eliminate the need for 1v4 situations anyway.
Hope you use this build well, have fun nuking!

Flash and ignite are best used, ignite can finish champs off that you didn't quite have the power/ultimate stacks to chase but often it allows you to ignite a low hp champ then leave to go for another enemy. Flash is used for escapes, if you mistakenly ultimate or chase into a difficult situation then it is usually possibly to go into your shroud then flash away. Your stealth will stay active for a brief period after flashing out so the distance you make by flashing can easily get you out.