jungletoad: I have this problem occassionally with an old game, but generally I don't.
The older generation is different in a number of ways:
1. Most obviously, the graphics aren't as "good". I put "good" in quotes, because sometimes I like old school graphics better, it just depends on what they did with what they had, but it is true that even the best looking of older games had lower resolutions, less detail, fewer lighting/shadow effects, etc. To get over this, I have to remind myself that I am playing this game for either the gameplay or story, not the graphics.
2. Everything I said in point 1 also applies to music and sound effects.
3. Older games often have clunkier user interfaces. Particularly if it's a game that is DOS-based and expects you to use a keyboard for everything that now you would more easily do with a mouse. With this, it's really a matter of patience. You have to forgive the UI for its place in the evolutionary history of UIs and just gain a proficiency at using the older UI.
Sometimes a new game just can't hold up over time though, no matter how you approach it. I can usual appreciate them from a historical context, but that doesn't necessarily mean I enjoy them or want to play them for long given how many great games have come out since. In that case, better to just cut your losses and move on to a different game (even if it is a time-honored classic).
I don't believe one bit in the whole "it has to be appreciated from a historical perspective" argument. Classics in any other medium are defined by their ability to speak to audiences of any era, not just in the time they were written. I don't see any reason why games should be different. And honestly, there are very few cases in which this isn't true--most games that are held up as classics still deserve their status, if you make a point to try and understand why they are so good. I mean, sure... if for example you start up System Shock 2 and expect it to play like Bioshock, then you're going to be disappointed. But if you take the time to understand what it's trying to do, get used to elements that might require more patience, and look past the outdated visuals, then you'll find the game has a wealth of things to offer that you simply do not get in newer games.
Not that I blame anyone for not wanting to take the effort to do this. Some people just want to play games to relax, and don't want to "work" for their entertainment. And that's perfectly fine, and perfectly understandable.