Yes, a car would be your best bet to get downtown. Your hotel is also near the Detroit Institute of Arts, so that could be something to do if you have non baseball time. The hotel may be able to shuttle you to Comerica, but it will be insane around the park. There are also traffic restrictions during games, so they can't get right up to the park. I would recommend having them drop you on Woodward near the Hockeytown Cafe which is right across the street. From there you can get to several places for food or drink. The Town Pump is directly behind Hockeytown. State Bar is just down the street. Cheli's Chili is around the corner (Kid Rock played there after the ALCS clincher - no wonder the line to get in was two blocks long). The Elwood is behind the scoreboard in left field - right next to Ford Field too. Keep heading south to Campus Maritus, Greektown and many more places.

Getting back your best bet might be a taxi, especially if you explore farther south. Should be a cheap ride, but again - might be tough to get one.

Getting into these places will be another issue with the crowds that will be down there. I'm saving my allowance to shoot for game six tickets if it could be a clincher. I was lucky enough to get standing room for the last ALCS from ticketmaster the morning before the game. It is very possible I will be sitting at the Detroiter Bar watching it though.