Hello, this will be a quick mini guide on how to lane and teamfight with akali and what runes items masteries and summoner spells to use. Many of it I learned from watching Westrice's stream and practicing in-game.

Pros:

-Good laning presence
-Strong burst
-Melee but shroud provides early survivability (until the enemy team gets an oracle)
-When paired with supports like shen and janna can kill entire teams.
-High mobility with ult and shroud juking
-Strong anti-carry

Cons:

-Oracles can shut her down
-If she doesn't snowball early game she can fall off late game.
-Strong laner but can be outlaned by some such as urgot, vlad once he gets level 9, etc..
-Requires some support to stay alive.

I invest in the 21 in offense for the ap per level, flat ad, and ignite mastery. I use the 9 in utility for increased buff duration, health regen, and increased xp gain.

I use flat ad reds and flat ap quints and blues so that I can have twin disiplines at level 1 without buying dorans or amp tomb, which allows me to get boots.

The seals help your late game survivability, which Akali lacks.

Start with brown boots. On your first back you shoul try to have enough for giant's belt and amp tomb. Next finish your Rylai's for the ap health and slow that synergies so well with Akali. After this you have a choice between sorc boots and merc treads. Use your judgement to determine which you need. After this start building your lichbane. Rylai's and Lichbane are core on Akali because it makes her burst extremely high with the lichbane proc and slow from rylais. After this I get guardian angel because by now it should be mid-late game and you start to get focused. By the time you finish that the game should be nearly over, but if not build rabadons for the huge ap buff, helping not only your Q and R but your lichbane proc. Then finish with a will of the ancients for the spell vamp aura which increases your survivability.

In order of best to not best (Only listing good pairs for akali)

Zilean- Zilean's ult helps Akali SO much in game. With it and GA she can have 3 lives making her a huge problem in fights because she can just kill everyone.

Janna- Her shield and ult are also very good for Akali, increasing her survivablilty.

Shen- See Janna, pretty much just his ult is nice.

Rammus- Helps akali to lock down carries and kill them quickly

Soraka- Her heals are nice but not game changing like zilean.

Sona- her ult can help, but so can other champions. Basically all she offers is a small heal and aoe disable, still strong nonetheless.

Malzahar- See Rammus

In laning Urgot is the biggest annoyance I've ever had to deal with on Akali. His e still locks on to you even in shroud, making her zoning much harder.

Lee sin- reveals you with e, making him a ganking threat.

Warwick- You can't burst him down cause he's too tanky but he can sure as hell ult you and have his team rape your ***.

Malz- See Warwick without the tankiness. The suppress really hurts.

Rammus- 3 second taunt is fcking annoying.

Tf- Annoying *** ganks, just broken op champion in the first place.

Q- Your bread and butter skill. Deals most of your damage if you get the proc off, devastating to squishy champions.

W- Helps survivability if they don't get an oracle since they can't see you :P. Also good zoning/laning tool. Good in 1v1 situations. A good thing to do if you get in a 1v1 is sit in shroud and q then wait for q cooldown and q again.

E- Pretty much only good for farm. I don't use it in teamfights since it doesn't refend energy in any way and you'll find yourself running out if you use it along with your q and r.

R- a great ult that counters champions with escapes like trist and corki. Use it in combination with your Q. First Q, wait till Q lands then use r and trigger Q is a great harass tool in laning phase post-6.

If you're against someone you can beat, pretty much anyone but vlad urgot and maybe irelia, then you should play aggresive. Harass with Q if they come up for a last hit an if you get them low enough don't be afraid to flash Q proc>ignite them (this is pre-6). Use your shroud to zone them and harass and don't forget to CS at the same time. Getting creeps is easy on akali since her Q is like free no cost high damage farmer. Once you hit 6 you want to go for a kill. Harass them as much as you can pre-6 and then immediatly wait for 2 stacks of your ult then go for it. Flash and ignite if necesary. After the first kill you'll begin dominating the lane and forcing recalls over and over again.

In teamfights akali's role is sort of an anti carry clean up person. You wait for initial bursts, then jump in on their biggest threat an try to kill him. Usually it will be their ranged dps. This will usually cause the enemy team to focus you, because they don't want their ranged carry to die. This is where zilean, guradian angel, janna, etc.. kick in. This is also why Akali almost needs support to be good. GA or not, she's still squishy and can be killed twice. So having a strong support on your team is extremely helpful. If the enemy team has a malz or ww buying a QSS would be a good idea to counter their ults. Don't initiate on AKali unless you know they don't have oracles, even then it's risky. Basically just blow up their carry and clean up the rest of their team.

Short answer: YES

Long answer: it has been proven that Akali is viable in ranked and competetive play. However, she does have a rather high skill cap and needs to be mastered. She also has trouble if her team has no support to back her up. She snowballs very well and bursts very hard, and overall contributes a strong anti carry to the team.