Going Commando or Up Your Arsenal, in other words, 2 & 3, are probably the best of the original quartet. R&C1 feels a *lot* like Spyro actually, not having either a camera locked to the player's back or strafing necessitates the weapons needing auto-targeting, or homing, or large AOE, and dealing with crowds of enemies feels pretty fiddly.
>is there a point where it starts to decline?
Ratchet & Clank, at its best, was about a balance of three things: shooting, platforming, puzzles. R&C4: Deadlocked ditched a lot of the first two and maximized on the third. likely because of Sony demanding increased focus on multiplayer to show off PS2's online capabilities. Up Your Arsenal had featured online multi, but with Deadlocked, that emphasis only increased. I won't say that Deadlocked isn't fun. Weapon modding is really expanded in this entry. In 1, each weapon got an upgrade that you bought that was just a power boost and changed the color of the attack. 2 introduced weapons that levelled up through use, and could then have upgrades bought for them. In 3, they could be levelled up to 5. In Deadlocked, weapons level to 10. Each level unlocks what is called an 'Alpha Mod Slot'. These can be filled with items that slightly increase damage, rate-of-fire, etc. Each weapon then has one 'Omega Mod Slot'. These are filled with items that drastically change a weapon, such as making it deal shock damage which chains to nearby enemies, or leave behind globs of lava. Both Alpha and Omega Mods are not permanent, and can be swapped out as needed.
However, the moddability of weapons (and also likely the fact that this game was meant for online) is meant to balance out the fact that this entry, despite being more shooter-heavy, actually has *less* weapons than previous entries. You have your shotgun, your assault rifle, your sniper rifle, and a few more, but you don't really get the weird situational weapons.