Mass Effect is probably the only one I'd buy a new game without question, just love the whole universe (pun intended) about it
Fallout would've been up there but 76 is apparently woeful (not bought it, though). Too many games with the likes of Mario. GTA is definitely a contender based on sheer scale and time I spent playing the classics. If you can call the Arkham games a franchise I'd happily throw that in the ring, too.