I rarely if ever play XBLA games...
Most games that I want are 800 points and not worth buying at that price. there are a good 30 or something games that I would buy at 400 points in a heartbeat but none of them at 800...
The other issue is I'm an achievement whore, and whether you agree with that gaming philosophy or not there are quite a lot of people who subscribe to it. Because MS decided to have XBLA trials leave they're ugly residue on your gamercard (no doubt a ploy to get you to buy the full game) I've created a separate silver account to try out XBLA games with.... and that means it's a big more of a hassle to play them, as a result I've stopped caring almost completely.
If the trials didn't leave their mark on your gamercard I would probably auto download and try them out every week. Instead I don't even bother anymore.
IMO the 5 things they need to do are:1. offer XBLA games at a sale price at some point, either drop the price a bit after X months, or even X years or maybe have a "half off week" where all the games are half price.
2. Remove the "feature" that leaves XBLA games on your card after a trial play... you don't put 0/1000 for retail demos so there is no reason to do it with XBLA trials.
3. Give something extra to Gold Subscribers. You don't need to give up the goods for free but maybe a 200 point monthly allowance or a straight up 10% off all Marketplace purchases would be good, and it would help along XBLA sales too where some people would be more likely to try out a game they might have passed up before.
4. If the Game is going to cost more than $15 offer it as a retail disc.... Lumines sales numbers were not up to snuff not due to lack of interest but because a fairly large segment of the market boycotted the release because you were charging $25 for a download. I also find the $30 worth of oblivion content rather ridiculously priced for intangible ownership.
5. Improve the way you check for bugs, ensure all achievements unlock and ensure that XBLA play is essentially lag free when connecting two people across the world. And if a developer wants to release a bug fix patch... LET THEM. It seems rather ridiculous how buggy some of the XBLA titles are, even more ridiculous when the developers make a public announcement that they've fixed the bug but we might not ever see it because MS is too busy to be bothered with the patch.