Just got done reading the thread on this question you started on DakkaDakka! Lots of good points both here and there. Assuming we are limiting the discussion to hobby games that we are playing for fun, for me what makes a good wargame is:
1. Appeal. Do I find the theme/era/setting interesting? I also roll a game's miniatures into this. If I'm not that interested in what the game is about, then I'll probably pass even if its the best ruleset ever written otherwise. For example, I don't have a lot of interest in ancient warfare. You're not likely to see me collecting many archers or chariots anytime soon. A new starship combat game, though? You have my immediate attention!
2. Availability. This includes how easy it is to get ahold of the rules and other components, as well as how easy it is to find people to play with. To a degree, it also factors in the price of the components, though the other characteristics I mentioned can balance that out. I would say that 40k is probably the single most available game on the market, despite how expensive it is to get into.
3. Fun. This one is the most subjective, and it really boils down to do I find the game to be an enjoyable one to play? I have trouble pinning this down on any one particular mechanic or design element; it's more of a holistic impression of the entirety of the game experience. I generally like integrated turns, for example, but if a game that otherwise works well seems to break down because of the integrated turn mechanic, then I'd rather see it have UGOIGO instead. I feel like BFG is a great example of this!
