Suggestions
First suggestion is for Bot matches to still continue to count toward daily goals like "Cast 20 creature spells." This may have just been a bug, but last night I finally completed the Color Challenges and played a game of Standard Ranked. Today I tried to play against the Bot while I was at work to complete the challenges, but they were no longer gaining completion. Being able to play the bot, which has no time limits, is useful for someone who works a lot.
Second suggestion, following from the first, is a game mode that isn't timed in that way. Something similar to how games like Words With Friends, have some mode where you can play on your own time. I just don't have much time on any given day to devote all of my attention to playing this.
Last, players should still receive some kind of reward for finishing a ranked game. While I won my game last night, I lost my second game of Standard Ranked earlier today, and received nothing for it. I didn't concede the match, but I still received nothing. This completely ruins the experience of playing a game like this. Being a bronze player and playing against another low-level bronze, I was completely run over by someone running a 3-color deck. They'd obviously invested money into their deck, despite being so low a level. I don't have extra funds to spend. The best I can hope for is earning credits through playing. And if I can't improve or expand my card base when I lose, it kills the incentive to play. Something, anything, but not nothing. Then, at least, there's something to incentivize playing even when you might lose.