I can't think of any games I'm likely to buy on theme alone, the game has to play well, and be fun with interesting rules.

But I'd say theme is extremely important - there are tons of games I will never own just because I hate the theme. Pretty much any pool, sports, or playing cards based themes are instant hard NOs. Willy Wonka, Elvira, KISS, Oktoberfest, WWE? Zero chance I'll ever own any of those, total crap themes imo... I'll play them on location, sure. It's slim pickings here in Georgia, there are pretty much no pins I wouldn't at least play a couple times when encountered.

Plenty of mediocre themes are great games, it's just another factor, but they can certainly be deal breakers for me. On some the theme is more important than others.