I don't know how old your monitor is but that is a problem that I had with my monitor. CRT's eventually just wear out. It got so bad that in some games even with the brightness and gamma maxed out I couldn't see things. Hope that helps.
Depending on your video card there should be a gamma setting slide bar under settings, advanced then the adapter name. You can use this to change the baseline gamma for all games to be brighter.
1). Set it so your worst game is just right.
2). Then go into the games that were ok and darken them down.
8 years is getting along there and the eelctron gun in the tube is probably wearing out, but if you can squeeze another year out of it you might as well. At the rate display prices are dropping, in another 11 months they will be paying us to take them away...
Some games like Tribes II just come out too dark even with the internal adjustment. Gamma "warps" the way the brightness and contrast signals are interpreted.
I was having the exact same problem with games being too dark. After you install Powerstrip 3.3 you can use hotkeys during gameplay to adjust gamma settings. (ctrl+alt++ for added brightness and ctrl+alt+- for reducted brightness) This is a great program and its shareware but you can use it as long as you want, no timelimit...
No more adjusting individual game notepad settings for gamma for each game you play.
How much time have you spent doing that.