Being a digital CCG is a big advantage, actually. There's huge opportunity in the digital CCG market right now, and five years from now I think we'll say 2013 was the year that DCCGs started taking off. If not 2012, even: look at how well Rage of Bahamut did (technically a card battler, but still relevant). Rage of Bahamut is falling off the charts now, but I believe that if a digital CCG were balanced and had a pro community (for e-sports), it could be evergreen, where you come out with new sets regularly. Magic, for instance, is on its 20th year.
I think one macro reason DCCGs are taking off now is that virtual goods games are more acceptable to Western audiences. It used to be people didn't want to pay real money for virtual goods, whereas now it's pretty much expected in most games.
If I were to do a CCG, I'd take serious inspiration from the German-style board game genre. #1. Use a Victory Point goal instead of "kill the other guy" so you have interesting 3+ player play. #2. Use market-type mechanics and lots of options to avoid mana screw type degeneracies.
That said, I've heard of CCGs failing for not having enough random luck... so take my advice with a huge grain of salt. If you optimize away all the luck, you take out of the fun and most players will say you've gone too far at that point.
The problem with most of these post-Magic CCGs is that they're too similar to Magic, which was groundbreaking in its time but couldn't benefit from the German-style aesthetic, largely because it hadn't developed yet.
Secondly, being online is a disadvantage. Cards are part of the experience. Also, physical cards make Magic's love/hate scarcity socially acceptable in a way that it won't be in an online game. The way to win is to make the online aspect an advantage instead by open sourcing it. However, that requires a lot in the way of community management. It'll be a lot of fun, but hard to scale.