- No second hand purchases I have never bought a second hand game
- Can't sell on completed games I have never traded in a game
- Can't rent games (massive deal for single player games) Not true I can still rent games im not sure about buying or are short SP blasts
- No price decay with age Not true they do drop in price but a lot slower I admit
- No competition so prices are fixed True but you can get discount MS credit and there is talk of the market place "keeping parity with stores"
- Can't lend games to friends Blame the anti MS group for that
- No nice collection on your shelf I see that as a plus I currently have over 80 360 games in a box in the loft
- No longevity to your collection (you rely on MS still allowing you access to downloadable games should you ever have to replace your console/HDD, games like MvC are already being pulled from 360's download service) Its a rare problem but I see your point
I think as it matures it will be more and more like steam with deep discount sales and more a more steam like system.
That and I am really really lazy and don't like getting up off my fat ass.
I'd like to note that I do use steam for all my PC games, so really price is the ultimate limiting factor for me.
Make regular dirt cheap sales for old games and I will completely change my tune!