Theme seemed to be the most important thing for people buying RPGs, with second being playstyle. There are several alternatives for tabletop RPGs, with themes like sci-fi, fantasy, Lovecraftian (cthulhu and such). There are also several different brands, each with its own playstyle and strictness on role playing, combat, etc.
A lot of these tabletop RPGs simply require that you buy at least the rule book, which costs around the same amount no matter which brand you choose. As such, cost is not terribly much of an issue. Now, if you have to buy a lot of expansion material in order to make the game interesting, then that's going to cause a problem.
Quality as well is a little less of an issue. Obviously the buyers like good art and well bound books, but since it's a game of imagination mostly, they don't require too much investment in physical aspects. The focus should be on the quality of gameplay.
How customers buy is mostly 50/50 between buying online or in a store. Again, since the games are based on rule books, all you NEED to invest in is the book, and probably some dice. You can invest in expansions and figurines, but they're not required. Still, they are good to keep in mind to keep my product new and entertaining. Something to note is that some people will go in store to look at the books, checking out rules and systems for the game, before deciding which one to buy. I'm not sure how to get my product into that search when it's going to be designed online.
The interesting thing about RPGs is how much they leave up to GM and player imagination. The rules are more of guidelines, and as such they are not necessarily vital to the enjoyment of the game. They're a big part, don't get me wrong. But according the people I've talked to, and by my own experience as well, the GM and players will most of the time make "homebrew" rules and requirements in order to gain their satisfaction. Again, if the set rules are too constricting or too far from a GM or player's personal style, they won't be satisfied. But if you make them loose enough without being too loose, then buyers will satisfy themselves.
I think the important thing to keep in mind is still "How do I get the word out?" How do I show people that this is an alternative when the game will be designed for online? I could maybe design an alpha version for in-person play, to be tested at events at game stores, then release the full version on line after instilling the desire in possible buyers. I don't know.
The reflection that players tend to be able to make the most out of their RPGs is a good thing to note. As long as I can show an efficient, entertaining method of play, they should be able to fill in the rest.