GTA 2 is the most overlooked game in the series, for two good reasons. It arrived when it was already clear that the next step would be in three dimensions, and critics said it added too little to the first GTA. Both are true, and both miss its most interesting feature.
That feature is the respect system. For the first time in the series, working for everyone was impossible — every completed job angered somebody else. The game forced the player to choose a side, an idea that returned five years later as gang warfare in San Andreas.
One further detail has kept GTA 2 in discussions ever since: the name of the protagonist in its promotional film.