Use your adcopy to call out YOUR MARKET... that's what adcopy is for anyways.
just to point out to gkemper90 that what Garrett is suggesting is that you bid on general keywords such as "halo 4", but have actual ad copy like "Buy Halo 4 now for only $9.99". In this strategy you target a wide audience but then filter it down to the buyers by using "buy it now" language, V.S. already aiming narrowly at people who are in a buying mood with "buy halo 4".
Whichever approach you choose, this decision making is where you earn your cash . My own suggestion would be to look whether there are already a lot of people taking either approach, and then take whichever doesn't have a lot of competitors that are doing the same.