If only all games had the option to slow them down...

Some do, such as the superb "Aurikon" for the PC:

http://www.oneswitch.org.uk/2/sd-shoot-em-ups.htm#intro

Some Emulators do for the PC, such as MAME:

http://www.oneswitch.org.uk/4/games/MAME.htm

And... with CPU Killer (www.cpukiller.com) or Mo'Slo (www.hpaa.com/moslo/) you can slow your entire PC down. This will not be the solution for all games, but is well worth trying.