It's got Side-Arms
Those two words speak for themselves, best coin-op in it's day by far. I put more twenties (you may call them quarters) into this machine than any other.
Of course the graphics don't hold up today, and games like Raiden have taken the Side-Arms game mechanics to new levels, but there was no better shoot-em-up to be played when Side-Arms was in the arcades.
The auto-fire pickup is a sight to behold, and you feel almost invicible while you have it. You also need to get the laser pickup to beat the bosses much quicker.
The music in Side-Arms is really classic stuff, it's right up there with Gyruss in terms of memorability, and the sounds are great too. I personally love synth-style sounds in games, and one of the best sounds in this game is the sound you hear when you die.
In my opinion this game really should have been on the first collection, along with Quiz and Dragons which would have made Vol 1 perfect.
My review scores are only relevant to Side-Arms, because when that games in the collection I care less about what comes with it, it stands alone. As always my scores for Graphics and Sound relate to the time period then, not Gears Of War.