I don't think cel shading gives it an anime feel at all really. Just more cartoonish, ESF doesn't need to be cartoonish. It looks good in Budokai, but they have the modeled auras and the ability to use ten times more polygons than HL can.
cell shadeing may look correct or extreamly cool but some modifications to models would probibly be needed to make it look fully anime ish but it could work. altohugh form a programming standpoint im not sure of the limits/capabilites or even what would be needed to implement cell shading. (i have never done much 3d programming) still learning C++ to tell be honest.
i dont think the hl engine capable of cel shading , but anyway, i think it would look pretty cool , with some cool melee moves it would look nice , i think they used cell shading in budokai cuz it represents the cartoon side of dbz , real models sucked like in budokai 1 , it was a good decision to go cell shading , tough it would be totally different on esf