Here's my tier list, including only games i've played, with commentary
Top Tier:
Blazing Lazers - Diverse weapons and killer soundtrack
Gate of Thunder - Fantastic graphics + sound: quintessential 16 bit shooter
Gradius II - Lots of nice effects, good use of the system
Image Fight - Best pure gameplay of any shoooter I've ever played
Image Fight II - Features redbook remixes of the music from the first game! Perfect sequel!
Lords of Thunder - Nice game to show your friends or Turbo-newbies. Would have done well if they had used different instruments for the music... something more like the original Rastan maybe
Mr. Heli - Very fun and unique game. Never played anything quite like it!
Override - Reminds of Image Fight, except with hordes of weak enemies instead of fewer really tough ones as found in Image Fight
R-Type - Great music, a true 80's classic
Second Tier (I admit I might like all of these even more if I spent more time with them):
Aero Blasters - 2 player simultaneous,
Barunba - My favorite of this group, underrated, creative gameplay
Dead Moon - Very cool boss battles
Download - Challenging
Dragon Spirit - Mixed land + ground attacks a la Xevious. Unique theme gets it some points.
Kyukyoku Tiger - Decent old school shooter, unspectacular
Ordyne - It's got a shop like Lords of Thunder, but it has a lame theme
Psycho Chaser - Need to play this one more, looks promising
Spriggan - Seems decent enough, haven't played it much
Super Star Soldier - Very nice graphics but uninteresting gameplay.
Trash bin:
Legion - Slow moving ship and fast moving enemies make this one super tough. Lame death noise helps make this game feel poorly made.
Rock On - Stupid looking ship and even stupider gameplay.