*sigh*
Ok, clearly you didn't read my above post.
So I'll make a few new statements.
The bottom line is that HL didn't need a good melee system because it was primarily a shooter game (like most of the mods you mentioned). Now, regarding JKII, its engine is based on the Q3TA engine. HL is mostly based on the Q2 engine but it has been heavily modified since its inception. Even the original JK had a good melee system for its day and that was based on the old skool Q1 engine.
So, whats my point?
My point is that just because HL didn't originally have a good melee system in the original game, doesn't mean it isn't possible to make a good, easy to operate melee system. The bottom line is what kind of effort a team is willing to put into it. Basically, it comes down to animations and code. What this means is that most other mods don't make a good melee system because it takes a LOT of extra effort because it requires a high number of extra animations than just say animated sprites for gun blasts.
As for how easy to operate it it is, I'm not a tester, but from what I've seen, it's lock on and if you're in range, ya drill 'em. There's also apparently sawtting ki blasts.
If that kind of thing is too complicated and hard to work... uh, you're a gamer why?
So to conclude, as far as melee in any game is concerned, it comes down to animations, code, and effort.
-Karrde-