I think that the biggest question heading into the season was defense, especially w/ Cabrera moving to 3rd, no sure 2nd baseman (w/ Inge as the lead horse according to Leyland), etc. etc. So far it hasn't been an issue whatsoever - leading the league in fielding percentage.
Every team has a question mark. I'll take a question mark in the 3rd-5th rotation spots given that Fister's injury doesn't linger through the season. So far, other than a blown slow start by Valverde and a horrible start by Sherzer the pitching has been respectable. Not great (aside from Verlander) but enough given the lineup and contributions from players like Avila and Jackson.
The Tigers have a very scary lineup. If Boesch starts stringing some hits like today it's only going to be getting harder for other teams to keep up. I can't wait for the next 6 games against the Central.