Akali isn't bad pre6 her q-e combo hurts if you get q to proc, but after 6 she can rape most nontanks with her ulti
just use shroud to poke with q auto attack combo also since they cant attack you in it unless its someone like a garen that can spin

her main downfall is that you need a team with strong cc(since tops and mids normally have cc) and she needs her own rune and often mastery page to get her passives at lvl 1

I haven't played akali a lot in 5's but i have a ranked team i play 3's with and she does well there when there's a squishy champ i can exploit. play passive till lvl 6 and then murder ppl