Yeah. No one knew who Blade was, outside of a few Marvel super-fans. And they were good movies, save the last one which was...dumb, which made a lot of money.
A Deadpool game, play wise, should be like somewhat DMC/God of War-ish in game play, since that's just a great set up that cannot be beat, in my opinion. Obviously, they need to tweak it, maybe even rebuild it to suit the main character, but it needs to control well and have lots of cool combos and shit like you can do with DMC and GoW. I would also throw in some Punisher elements, like interrogations/torture and stuff. He should have the ability to use pistols, shotguns, assault rifles, swords, knives, shurikens, grenades, unarmed combat and pick up random things from the environment to use.
They should use an original story for the game, take elements from previous comic storylines, but don't outright mimic one. If possible, get some of the writers who've handled him to give some input. In the game he should clash with Weapon X and SHIELD. I think he should also go up against Arcade--Arcade's modus operandi would allow for some really neat levels and stuff to play on, and maybe some stuff with Loki--just as a change of pace from the usual merc stuff.
Bosses: Bullseye, Punisher, Taskmaster, Typhoid Mary, T-Ray, Wolverine, Cable, Sabretooth, Garrison Kane, Shen Kuei--The Cat, and who knows?
It should be Deadpool wreaking havoc anywhere possible and kicking everyone's ass. It should be fun, intuitive and need continuity in no way, while still introducing other characters with long histories with Deadpool to please the fans.