Nearly all 3rd party apps not working

This is really frustrating and a huge time-waster. I'm using an SPH-M800 Instinct phone. I can go to any 3rd party app site like getjar.com, mobilerated.com, instinctapplications.com, etc. If I'm doing it through the phone's browser the site will auto detect the phone model automatically and if I'm doing it on my PC I set the phone model manually. All seems well at this point.

Now I'm assuming that the reason for doing this is so that the apps/games presented to me will be ones that will work with my phone. However nearly every app/game that I've installed does not run properly. They don't all fail in the same way. A few refuse to run at all, some have problems with the controls, some will run once then refuse to run after that, some lock the phone up, etc. There seems to be no end to the ways in which these apps fail to operate properly.

So what's going on here? What's the point in specifying my phone model if the list of apps presented to me won't run on my phone? I don't see where I could be doing anything wrong. Most of the sites will list the compatible phone models for a given app and the M800 is invariably listed as one of them.

To put things in perspective, I've just spent the better part of 12 hours installing upwards of 60 apps/games and so far I've had to uninstall all but 4 of them because they wouldn't run properly for one reason or another. Aggravating to say the least.

Can someone please lend some insight?
Barring that, are there any sites with free apps/games that will actually run on my phone without having to go through this tedious trial and error process?

Thanks in advance,

tgeer