Genesis and the Saturn. I never get tired of Streets of Rage.
Love the Mega Drive:
Thunderforces 2,3,4 - 3 being my all time fave shooter
Gaiares
Musha Aleste
Gynoug
Bio Hazard Battle
The Toaplan conversions - Twin Cobra, Zero Wing, Hellfire, Fire Shark, Twin Hawk
To name a few, there are so many others
OK, not the bullet hell / bullet curtain shooters of late, but great blasts easily available at reasonable prices.
Currently trying to track down a Thunderforce AC PCB to stick in one of my cabs - not an easy one to find.
Have you played it? It's basically a "different" (I wouldn't say better) TF3 without the stage select that seems to be based on S16 hardware.
Thunder Spirits on the SNES seems to be a conversion of it. TF3 original is better than both IMO. But hey, it'd still be a cool board to have.
Oh, and I forgot to mention the most underrated shoot on MD - Granada. Imagine Gauntlet with tanks...