I'm assuming that different Tavern patrons here have different requirements of what makes a good game store, much less a Favorite Local Game Store (FLGS).
For some dumb reason I tend to pick up way more board games than I get to play (so....most of them) and any store that wants to contend for my FLGS title has to have a decent spread of board games. If I can't find a good half-dozen Spiel des Jahres (German Game of the Year), then they're right out. If 75% plus of the business is Collectible Card Games, which is usually immediately evident, again....right out.
A good game store, has some used games available, and if they have some games (really, ANY games) available to demo......they get on my short list. I think one of the most important services a FLGS offers is serving as a connection spot for gamers. They don't really need a ton of gaming space, but a table or two for demos or a friendly game is a HUGE plus. Some kind of bulletin board for groups seeking players or players seeking groups really helps.
As far as stock goes, yes....I'd love to be able to find used products so I can try or have a place to offload some games I know I'm not going to ever get to play. That's a minor thing.....what is major for me is being able to find new games and expansions that I didn't even know about. Being able to grab some minis or paint supplies is just about required. I don't need to see a large supply of minis, but a mix of PCs, monsters, and terrain is a must if there's going to be any.
Since I travel...a lot, I've seen more than my fair share of stores. Most aren't worth mentioning and some don't seem that great on a quick view, but spend a few minutes checking things out reveal a FLGS in the making. I've noticed many game stores service the local nerd community with more than just games.....a lot have comics as well. A few more might have food and a rare few have a bar! I've seen game stores with a small arcade and one Hastur Games (SLC area) has/had (haven't been there in at least half a decade) had a row of computers for local LAN games or online play.
So...what do you require in a game store, much less a FLGS?