With Temporal Striker, I think it's pretty good:
Turn 1: 4
+ 4
= 12 damage
Turn 2: 2
= 24 damage unupped/36 damage upped [time bubble, 3/5 turns]
Turn 3: 4 damage, out of time bubble [unupped]/1 turn of time bubble left [upped]
Mostly burst damage, but I think that 48 damage is quite worrisome in terms of balancing. It could make time/life quite dangerous.
*Note: Someone [I think willng3] posted in the game suggestions about a bug with sundial & acceleration. Apparently, sundial will treat all creatures' attack as 0 for one turn; this means that andrenaline will undergo 5 turns of attacking, which would mean an instant out for Temporal Striker. Just something to think about when balancing this card.