Among other large-scale issues on the agenda, Walker says the Spy's disguise has nearly reached the end of its lifetime. Over time, average players have become much better at detecting and dispatching disguised Spies, making the ability pretty useless for all but the sneakiest of players.
Additionally, Walker feels the Engineer's sentry guns have become "too binary." They're highly lethal to some players and wholly ineffective against others. Sentry guns are also easily dispatched by skilled players, leaving Engineers with little recourse. Keeping a delicate balance is important, as is adjusting problems that arise from the way players utilize the different abilities of each class in the game.
For a load more fascinating information, it highly recommended you check out the entire interview.
