I think there should be a time limit in games. Got to a 1v1 but neither had any ammo, just bazooka and were so far apart took ages to eventually hit each other. good game though :)
I really like this game. Though I think it would be absolutely awesome to make it multiplayer online. Using an ELO system for ratings (a league may be too much). Would really take the game to the next level.
Please look into the match up system in the arena. You get some really unfair match ups, either you're against a level 50 guy when you're level 30 or vice versa...
I really like this game... but the PvP needs to change. Biggest issue is that you can fight pretty much any level. So for 10 fights in a row you're against level 50 guys with unbeatable decks at your level... really drags it down.