There downfall was trying to break into the console market. Like the Phantom they wanted to offer everyone's games on one console. Which only would have worked if they got the rights to a platforms exclusive titles. So if you wanted to play Xbox, Wii, and PS3 games without having to buy all three consoles Onlive would have been a banging deal for only a hundred bucks and a small monthly fee.
Personally they should pull out of the console market entirely and focus on a PC service only. This would be amazing to allow people with strapped budgets to play high profile games without having to shell out hundreds of dollars on computer upgrades. Not to mention this would probably drive hardware prices down in the long run.