I think Gun*Nac is actually the worst of Compile's NES shooters. Their others, Zanac and Guardian Legend, are both legitimate classics. Also look into their games for other systems (M.U.S.H.A., Space Megaforce).
Look for anything by Cave (DoDonPachi, ESPGaluda, etc.) or Treasure (Radiant Silvergun, Ikaruga).
Gradius V is perhaps the best in the series (that or Gaiden, which is still import-only =( ), and if you have MAME, 3 is worth a look just because it's supposedly the hardest game ever (I mean, Battletoads and Bayou Billy have NOTHING on this mutha). Also on the topic of Konami, Salamander/Life Force (arcade) is the absolute best of their old-school shmups IMO.
The R-Type series, of course, is generally awesome as well although there are a couple clunkers.
-Josh
but then you take my 75 perchance chance of winning, if we was to go one-on-one, and then add 66 and two-thirds ch...percents...i got a 141 and two-thirds chance of winning at sacrifice