Where to get help choosing older PC games?

Good Old Games is a great place to buy older PC games, they're all DRM-free and patched/modified to run on modern OSes. The community is also great in general, and a lot of the game reviews are very well-written. They have a new feature too that lets people set up "GOG mixes" which are basically groups of games, so if you can find one including games you already like, you'd probably like any others in the same group.

The biggest hassle with older games tends to be a lack of widescreen monitor support by many (but not all) games from before 2004 or so.

Widescreengamingforum.com has a list of many older games with widescreen issues and solutions which I have found very handy.

Another thing you can do is look for web critics who review old games (such as Spoony at spoonyexperiment.com). Amazon.com has a wide selection of old PC games listed and you can have them listed by rating, but this doesn't have the best quality. Another option is to read modern PC gaming magazines. This might seem counter-intuitive but I found that they would frequently refer to games that the writers of the articles did or didn't like and even use older games for benchmarking.

I would like to note that I haven't read many gaming magazines recently, so that might have changed.