God of War: Chains of Olympus after finishing 3.
I hadn't played this in ages, and I was hankering for more of that sweet, sweet combat. Of the two PSP titles I think it's the superior one. Ghost of Sparta is alright, but it has some of the blandest, most forgettable level design in the entire series. Chains of Olympus is shorter, but it feels like the right length and never outstays its welcome. The few new weapons and spells there are are fun, and mostly avoid feeling like reskins of other abilities. The Gauntlet of Zeus is an especially satisfying weapon. Though it's a bit short on boss fights for the series, the few there are are very nice, and the final boss feels like one of the hardest in the entire series.
It would be tempting to call it little more than a glorified God of War 2 level pack, but it actually manages to build the continuity and Kratos's characterization in pretty significant ways so it feels like a vital piece of the series. Since it's a prequel, Kratos acts surprisingly humanely in it compared to most other entries, feeling more like a harsh enforcer of Olympus than the spiteful, omnicidal asshole he becomes later. It also has one of the strangest but most memorable uses of the button mashing prompt ever, abandoning your daughter in Elysium. It's one of the only times I can think of where using a quicktime event actually feels perfectly meshed with the story, since Kratos has to struggle to be able to get through.
It has some shortcomings though: the aforementioned dearth of boss fights is noticeable in a series known for them, the fact that we never even see Morpheus despite him being the main threat for like half the game feels dumb, there's hardly any new music (if at all), and I think out of all the games in the series pre-reboot this one has the most problematic camera. There's one combat section in particular towards the end where I died at least a dozen times: you're locked in a room with to Minotaur giants that have a charging attack that you can't block, so you have to dodge it at the right time. The problem is that almost always at least one of the Minotaurs will be off screen because of the camera, and as such you have no plausible way to see what they're doing. This led to another particularly aggravating revelation: if you die enough times in the same section, the game will just give you extra health. Unprompted, unasked. I can't remember the last time I felt so condescended to by a game.
Over time one thing about these PSP games becomes just more bewildering: what other game series has made allusions and references to events that happen in games that weren't even out at the time? God of War 2 mentions Kratos putting Atlas in the position he's in, but Chains of Olympus came out about a year after God of War 2. God of War 3 makes some very noticeable references to Ghost of Sparta ("Your pawn has failed you, Gaia. Perhaps you should have chosen the other one."), but that game hadn't even been announced when GOW3 came out. We even hear a couple of lines directly from Ghost of Sparta in one sequence.