I'm not really sure who asked for the Ratchet & Clank series to focus on cooperative play, but it certainly wasn't me. I'm a big fan of the Lombax's previous space adventures, with the series managing to combine some good old-fashioned platforming with excellent projectile and melee combat. I really didn't want Insomniac to ditch this formula in favour of four-player co-op, fixed camera angles and simplified gameplay. But that's what we've got.
Those aspects sound like your kind of thing? Ratchet & Clank: All 4 One carries them off pretty well.
As you might expect if you've been following the series, the evil Dr. Nefarious hatches a plan to destroy Ratchet, Clank, and Captain Qwark, but things go wrong. The quartet are kidnapped by new villain Ephemeris the Creature Collector, sent to the planet Magnus and forced to work together in order to fight against this new foe. It's a little contrived, but the four main characters had to be put together somehow.
On some levels All 4 One plays a lot like its predecessors. You still acquire a massive arsenal of inventive weapons (most of which you'll have come across before if you're a long-time fan), which is pretty much the series' trademark feature. Weapons such as Mr Zurkon and the Warmonger are joined by new tools, including a slime gun, pneumatic drill, reflector shield and a multi-purpose hoover. It's the latter that proves most useful, being called upon time and time again to interact with switches.
Combat is good fun, with the variety of weapons making for an explosive mix (especially with four players all going at it either locally or online), but there's no denying that things have been dumbed down compared to previous Ratchet & Clank titles. While new enemies are constantly introduced over the course of the adventure, they rarely require anything more than a few moments of sustained auto-targeted fire - or a special conjoined stream of fire caused when players all target an enemy with the same weapon.
Sadly the weapon-levelling system seen in previous titles is gone - replaced with a simplistic three-tier system which requires you to redeem collected bolts. As a result I found there wasn't nearly as much incentive to switch between weapons, instead choosing to focus on the one I'd already fully levelled up.