It lasted me 4 hours but probably 1 hour just for that fucking "Vidi, Vici, Veni" part lol.
I have it both on 3DS and PC, and yeah, unless you really want to play it on the go, the PC is more attractive price-wise. I bought it for 1.49.
I think it fits well on the 3DS but I have a hard time recommending it for 8 or 9 $ or what it costs. And yes, I'm just that good that I beat the game pretty fast in one sitting.
Ongoing bet with think-man: He wins if MH4 releases in any shape or form on PSV in 2013, I win if it doesn't.