It's really hard to say without knowing specifically what previous ROM you were using, but there are two possibilities I can think of:

 1. The apps in question were updated to require some new feature that your device doesn't have.
 2. (Probably more likely) Your previous ROM had different information in the `build.prop` file than your current one does. This can include specific hardware like GPS, NFC, accelerometer and such or things like screen density.

The `/system/build.prop` file contains a lot of information about the hardware of your device (among other things), and it's what the Play Store will use to determine if your device supports the hardware requirements of a given app. It is fairly common for ROMs to use `build.prop` entries to masquerade as other devices or pretend to support nonexistent hardware for the sake of app compatibility. I would suggest trying to find a copy of your old ROM in zip format then extracting the `build.prop` from your old ROM and comparing it to your current one. If they are different then you can consider editing your current `build.prop` to include any missing entries from the old one ([there are apps to help you do this][1]). This is also covered in some detail in http://android.stackexchange.com/questions/5078/is-there-a-way-to-trick-the-android-market-into-thinking-im-using-a-different-d

For screen/LCD density specifically there are [a handful of apps][2] that will help you modify it. Based on [Chahk's comment][3], values of 160 and 240 may be good to try if it is set to something different than that.


  [1]: http://forum.xda-developers.com/showthread.php?t=1479703
  [2]: https://play.google.com/store/search?q=lcd%20density&c=apps
  [3]: http://android.stackexchange.com/questions/21580/incompatible-apps-through-google-play-market/21581#comment25100_21581