Achilles is a very simple beat-'em-up in the classic tradition of such games as Final Fight. You play the titular Greek hero, and move along an endless beach featuring a plentiful quantity of people to stab and slash. You begin armed with a spear, which you can poke at enemies or throw at them; once you've thrown your spear, you start using your sword. You can pick up more spears (only one at a time, though) from fallen spearmen. You can also kick enemies to stun them, and you have a shield which can block most of most blows. A single enemy is generally not much of a threat (although if you give him an opening, he can do a fair amount of damage), but if multiple enemies jump you simultaneously (especially since they can approach from both directions), you can very quickly be overwhelmed.
Your character's attacks are somewhat unpredictable. Pressing forward + attack yields a different attack than simply pressing the attack button, but each has several different possible attacks which can happen seemingly at random, and the damage that these attacks do ranges from minimal to instant decapitation, so there's a lot of randomness in how quickly you can dispatch an opponent, and since this speed is critical to surviving, you'll end up with a fair amount of randomness in your outcomes.
The game offers two modes: in the story mode, you face a finite number of enemies per level; at the end of every stage (each stage contains three levels), there is a boss. In survival mode, you simply face an infinite number of the three basic types of enemies (swordsman, spearman, and archer). Since the basic gameplay is exactly thes same (as you pass through the five levels of story mode, the appearance of the opposing soldiers changes, but that's about it), this doesn't add that much to the game.
The graphics are pretty basic, with lots and lots of blood spurting from your enemies as they are impaled with spears, decapitated, or suffer other gruesome deaths. The sounds are also pretty basic, and the background music (during the levels) is just drums, which gets awfully repetitive and wearying pretty quickly.
Anyway, Achilles is a fun way to enjoy hacking up people for maybe a minute or so, but the repetitive and very limited gameplay coupled with the extreme randomness mean that this just isn't a terribly interesting game in the long run.