It's not so much that the newer ones are worse, it's just that they are all basically just Armageddon again with some stuff tweaked or a handful of new weapons.
At least that's how it appears, I'll admit I have not played Revolution. Have they added anything significantly expansive or different?
I think that's the one where you have four classes of worm and you have to gain coin crates that drop in order to purchase weapons.
Also, they screwed up the ninja rope. It's now got rope physics.
Having only looked at the trailer video, Revolution is indeed the one with multiple classes, and it seems to imply that they have different amounts of weapons, equipment and health.
Ah, hell, I mixed up Revolution and Reloaded. Dammit, alliteration in sequel names. Revolution is basically Armageddon with new graphics, maps, and some new weapons.
Actually, only Reloaded is Armageddon once again. Worms World Party was actually a (IIRC cut down) version of Armageddon for Dreamcast, which got ported to PC and GBA. Similarly, Open Warfare was basically Armageddon for DS and PSP.
After WWP, a series of 3D games were released (3D, Forts, Mayhem, then the first and the third got glued together with updated graphics as Ultimate Mayhem), so, totally not like Armageddon, and after Reloaded, they went into the classes thing with Revolution and Clan Wars.