Maybe the most classic genre there is, the Shoot'em up, here in a great French documentary.
Interviews with Cave and Grev, lots about Treasure and the other greats
Documentary Link.

It is a genre with many subgenres.
- Verticalscrollers, which are often divided in tactical shooters like the great Raiden series and manic shooter's like cave's
- Donpachi series
- Horizontal shooters
- Fixed Shooters
etc.





The top 25 shoot'em ups according to shmups.com


[01]  Dodonpachi (ARC/PS1/SAT) 
                               
[02]  Gradius V (PS2)                 
                       
[03]  Battle Garegga (ARC/SAT)         
                         
[04]  Armed Police Batrider (ARC)                               
[05]  Ikaruga (ARC/DC/GC)                   
[06]  Radiant Silvergun (ARC/SAT)
[07]  Raiden DX (ARC/PS1)                   
[08]  ESPGaluda (ARC/PS2)           
[09]  Shikigami no Shiro 2 / Castle Shikigami 2 (ARC/PS2/DC/GC)   
[10]  Dodonpachi Daioujou (ARC/PS2)       
[11]  Border Down (ARC/DC)           
[12]  Thunderforce III (GEN/SAT)       
[13]  Rayforce / Layer Section (et al) (ARC/SAT)       
[14]  Gradius Gaiden (PS1) 
[15]  ESPRade (ARC)     
[16]  Gunbird 2 (ARC/DC/PS2)     
[17]  Mushihimesama (ARC/PS2)   
[18]  R-Type Delta (PS1)         
[19]  Mars Matrix (ARC/DC)   
[20]  Giga Wing (ARC/DC)   
[21]  Batsugun / Batsugun Special Version (ARC/SAT)   
[22]  Soukyugurentai (ARC/SAT/PS1) 
[23]  Einhänder (PS1)   
[24]  Thunderforce IV / Lightening Force (GEN/SAT) 

Webzine way of the rodent made a Top 50 in their 50th issue as well, with some lovely hagiographies in the article.
They used a slightly different definition, and made Robotron their nr. 1, as you can read here

  • Robotron
  • Space Invaders
  • Defender
  • Tempest
  • Rez
  • Star Wars
  • Galaxian
  • Gradius
  • Ikaruga
  • Asteroids
  • R-Type
  • Doom
  • Centipede
  • Missile Command
  • Sinistar
  • Star Force
  • Tempest 2000
  • Galaga
  • Moon Cresta
  • Llamatron
  • Uridium
  • Metal Slug
  • Geometry Wars
  • Scramble
  • Afterburner
  • Jet Pac
  • Xevious
  • Commando
  • Radiant Silvergun
  • Juno First
  • Phoenix
  • Bangai-O
  • Drop Zone
  • Vanguard
  • Viewpoint
  • Gunhed
  • Gorf
  • Delta
  • Swiv
  • Side Arms
  • Thunderforce IV
  • Battle Squadron
  • Pulstar
  • Mad Planets
  • Encounter
  • Einhander
  • Matrix
  • Gyruss
  • 1942
  • Armalyte