What, no one here liked Target: Earth? To this day that's one of my favorite side-scrollers ever, simply because the art was cool, you actually had ALLIES fighting beside you (no more one man vs an army) and I'm a sucker for run-and-gun games.
I mean, the 8th stage had you flying through space fighting other mecha with a backdrop of a giant Earth fleet of ships (probably in the range of 20 or ships including the command ship which was like... 3 screens long) vs a fleet of alien ships (even more ships and a mothership that was 6 screens wide or something) all of whom were firing at each other while their respective mecha fought in their shadows.
Flying through stage 8 with capital ships blasting away on all sides and you, your buddies and the enemy all dogfighting while it goes on is STILL one of my best game experiences in a side-scrolling game... Target: Earth just felt truly epic, especially in that last space battle stage.