Let me start by saying I am a HUGE fan of the Ratchet & Clank series, ever since the very first game that came out in November 2002 (which I played at a friend's house in 2003). I have always been excited for new releases and, up until now, have never been let down by any of the Ratchet & Clank games. Insomniac really let me down on this one though..
I was well aware that All 4 One was intended to be a co-op game, which is fair enough and is not the reason why the game let me down, as single player is still available. All the ingredients that make Ratchet & Clank games so compelling seem to have all been removed from All 4 One. For a start, one ridiculous feature is the inability to even rotate the camera. The right analog stick has been changed to the 'Quick Select' wheel and the triangle button is no longer used to select weapons but rather, uses the 'Swingshot', a gadget Ratchet & Clank fans will be very familiar with. The inability to rotate the camera angle confines you to a very linear, restricted path; you seem to lose all the fun of exploration of hidden areas that previous games in the franchise had. For the first time in any Ratchet & Clank game (I exclude 'Size Matters', 'Secret Agent Clank' and any other PSP games, as I have never owned a PSP and so haven't been able to play these), you cannot use the circle button to shoot! Instead, it is used for some hoover-like gadget called the 'Vac-U' which sucks up critters and can be used to break crates.
Weapon upgrades. From playing a significant amount of time, I noticed that my weapons don't seem to upgrade with frequent use, which has been in every single PlayStation console game (perhaps excluding the PSP ones?) since Ratchet & Clank 2 for the PS2. You are able to purchase upgrades such as increased ammo capacity, damage, etc. from the vendor, but it doesn't compare to the fun, enjoyment and genuine excitement you receive from upgrading a weapon whilst in the middle of an intense battle, say. Ammo is also restocked from 'Ammo Pads', which completely restock all your ammunition to maximum capacity; we don't get ammo crates anymore. Health is no longer numerical like it has been for some past few games, rather, you have 3 chevron-shaped health slots (this may increase later in the game) and then upon dying you seem to respawn a few seconds later in the same spot, providing your buddy (in my case for single-player, Clank) doesn't die.
It's fair enough that L1 doesn't use first-person view and instead is used to lock-on, as the game is designed for co-operative gameplay. What I don't like is the co-op shooting damage bonus, whereby shooting at large enemies whilst your buddy is also shooting them cause rings which expand and provide a massive damage boost when at maximum size. They are ugly and not pleasant to look at, regrettably, like most of the features in All 4 One, whose graphics I'd say are not even on a par with the original Ratchet & Clank for the PS2.
If I were designing co-operative gameplay, I'd look more on the side of Ratchet: Deadlocked (Gladiator in UK) co-operative gameplay, which was different, but still very fun. You still had the same great 3D environments like before and weren't restricted to a set path and were able to rotate the camera (although you couldn't leave your friend too far away or you'd both be killed by the Deadlock collar) to look around in split-screen. On a final, negative note, whatever happened to flying between planets (or through sectors as it were in 'A Crack In Time')? I seemed to get the impression that levels on this game are based on a very generic, level-based system like in the oldest console games, rather than the elegant planet-based system seen in all previous games.
Overall, I'd conclude by saying that generally, this game is a disappointment to any hardcore Ratchet & Clank such as myself. I was hugely excited by the release of the game and was actually more excited than not about co-op gameplay, as I thought it had great potential after playing games such Ratchet & Clank: Deadlocked, as well as a similar split-screen type system for the Multiplayer in Ratchet & Clank 3. There was no need to change the controls around; keeping the old-school controls as well as R1 for shoot would've been fine and having a rotatable camera in either split or shared screen would've been more desirable. Quick Select? Should definitely still be triangle, then L1 and R1 for scrolling weapons. Weapons should be upgradable with frequent use; any additional modifications like extra ammo etc. could just be bought using raritanium, like in Ratchet & Clank: Tools of Destruction. Gameplay seems very repetitive. Wasted potential for what I'd hoped would be such a great game. I just hope all Ratchet & Clank games to come revert to the old-style gameplay, as Ratchet & Clank is a franchise I never want to see die. I suppose for such a great franchise I can forgive Insomniac for this slip, but seriously guys, give us the old gameplay we know and love back; it was epic and provided me with no end of hours of fun. Heck, even after I beat the game, maxed out every weapon and acquired all the gold bolts, I still went to go for a run around on challenge mode to farm as many bolts as I could without losing my x20 multiplier! :D