GameFAQs. But then again you said "good"
I'm joking - I would recommend it but with a catch - GameFAQs is not a singular entity - it's a collection of different games that have attached boards (forums). There are also some not-specific-game-game-related-but-of-somewhat-related-interest boards, like "Pencil+Paper RPGs", "Creative Writing", "Game Design and Programming" and so on. The actual quality per game (and/or board) varies. Especially with popularity - dead boards are not really good (duh) but really active ones may be infected by trolls (though that's not that bug of an issue). If the game you're interested in has an active forum, you could jump in and start discussions - I've found that people do like discussing stuff. Not really surprising, as they'd be visiting the specific forums for, most likely, that reason.
The games themselves have an FAQs section (It's Game
FAQs after all) which is not really appropriately named for it's mainly for user submitted guides. These range in size, topics they address and completeness but in general, I've found the majority of them to be good. What they handle is usually walkthroughs although some are more specialised, like character creation or specific system of the game (e.g., combat). What you might be interested in is the plot analysis guides - there aren't that many of them but they tend to be quite good. I still think LOKFanatic's Plot Guide [http://www.gamefaqs.com/ps2/914777-legacy-of-kain-defiance/faqs/25247] for the Legacy of Kain series is top notch. It's quite thorough and could be used instead of playing the games as it does convey the plot as well as give other comments and analysis on it. It's not even the cliff notes, it's quite thorough.
It may be a hit and miss depending on which games and/or topics you're after but I've personally been a member for a decade now[footnote]actually a bit longer, but my first account got...lost. Or something.[/footnote] and I've found it useful when it delivers.
