First of all the game and especially the design of the cards are awesome, so every critism is critism on a very high level
I personally think it's a bit too easy to collect points. For example I have lots of good cards and could buy Gold Packs with good players all week. I would prefer if every member would choose 5 cards, let's say 1 Top 10, 2 Top 20 and 2 Top 50 and then plays with them for a half year. Then the member who has chosen the best team will be ranked first. After a half year there will be a big trade and everyone will have the opportunity to trade cards. Of course you could still buy the surface cards which would reduce your ranking.
For example a player who would have choosen this team at the start of the year would be ranked very high now:
1 Top 10: Caroline Wozniacki
2 Top 20: Li Na, Maria Sharapova
2 Top 50: Andrea Petkovic, Petra Kvitova
I know it's not really entertaining thorough the year and the system isn't fully developped yet but something like this would be cool