Was it the noob lock on guns, the gigantic hit boxes or the horrible dual wielding that made it the best, i forget.
Noob lock on guns? Really dude? That's the best criticism you can come up with? Yes, it had its issues, but so do the other games. I can say this, it didn't have annoying, near game-breaking armor abilities like Jetpack or Active Camo. It didn't have inconsistent equipment that was the definition of "noob" entitlement. Shoot a guy three times, he hits a button and shits out a regen and then kills you. Skill(tm). It didn't have ridiculously over-powered vehicles or an even more ridiculously over-powered and broken anti-vehicle weapon.
It did have an inconsistent shotgun that worked only for the host, broken button combos and the sword, which as someone who used it frequently, was broken. Dual wielding wasn't an issue and actually gave a variety to the combat that hasn't been seen since. It also had the best maps in the whole damn series that have yet to be topped. And even when Bungle tried to remake them, they ended up fucking them up. Also, it had the best Battle Rifle in the series.