Some friend groups seem to require an excuse to meet up. Hardly anyone I know watches sports, alcohol is best used rarely, if ever, and just having dinner feels a bit too aristocratic. Watching movies used to be good, but nobody seems to have the patience for that anymore. Having no imagination doesn't help either. Since I live in Finland, sauna has been my go-to activity. Unfortunately, I have not-so-recently hypothesized that the mysterious headaches bothering me might get triggered by it, so I'm limiting myself to two or so per week. Enough to retain my citizenship, yet rare enough to confirm my suspicions. So board games it is.
You Play to Win the Game, Zvi writes, already summarizes most of my thoughts about the topic, but I'll discuss some of my own observations. The most interesting of them so far is that often people have different goals, even if the rules are the same for everyone.
Having fun is quite important. Winning is fun, of course, and doubly so if you can make it look clever. Some games emphasize the actual win condition more, while in others, strategies that are unlikely to win are more interesting to play. Often, if it's too easy, it's not enjoyable anymore, so a stronger player might pick a self-imposed challenge to keep it interesting without having to hold back.
Personally, I don't enjoy thinking ahead too much. It's tedious and slows down the game a lot. Some of my friends really only play this way, which is at times quite frustrating. Especially because it means I'll rarely win against them. You could potentially solve that with a clock, and chess does this pretty well, but that would feel too heavy-handed for games that I think of as social lubricant instead of a puzzle. And it's way better than the alternative, making nonsensical moves and not even trying to win.
One interesting technique I've been experimenting with is taking variance-increasing (high-risk, high-reward) moves when you're expecting a loss if you play normally. Scoring even a single game against a stronger opponent is quite satisfying. Not all games allow strategies like this, but when they do identifying them is part of the fun.
Some games repeatedly end up in positions where two players are competing for the victory, and a third player can decide which one of them wins, but have no shot at it themselves. In general, I feel like games should be designed in a way where, as long as you're allowed to take actions that affect others, there is some way you could still win, even if the odds are really bad. On the other hand, it's quite frustrating if playing better doesn't guarantee winning. With two-player games, resignation is often an option, but when more players are involved it's rarely the case.
I only like cooperative games if everyone has different information. Otherwise, it just becomes the best player solitaire-ing. Or everyone arguing about the best line. I think Hanabi and The Crew succeed quite well in this.
Semi-cooperatives, typically with hidden per-player win conditions, can achieve the best of both worlds, when carefully balanced. The only good example I can think of is the Nemesis series. Cooperative play is still the default, but everyone has to be wary of a backstab until the very end.