Gameplay-wise, most Armored Core games have been only thinly distinguishable from sequel to sequel. You're a mercenary with a great big mech, which you can customize to your heart's content. Last Raven does bring a few more sandwiches to the picnic, but it's really just another small upgrade in a series that runs short on big ideas.
Since the developers know that their fans are hardcore as hardcore gets, metalheads are unceremoniously dumped in the deep end with no tutorial. You do get two options this time around: you can challenge a ladder of over 30 head-to-head arena bouts or explore a storyline that branches based on which of the over 70 missions are completed. The tale unfolds through e-mails, text-based reports and the most rudimentary of in-engine cutscenes, though, so don't let the slick opening movie fool you.
While the campaign mode is certainly welcome after the previous AC game's arena-only focus, its missions and level designs have a dull, prefabricated feel that makes it hard to get interested. Stark environments are granted only rudimentary details and texturing, and populated with helicopters and pointless human specks that are only barely identifiable as such. Enemy mechs look better, but they tend to just hop around, firing maniacally. The game runs well, but the hit to the detail makes it hard to care. Worse, the objectives - protect this bland base, accompany that easily destroyed gimp - are executed with zero imagination, and no regard for any consistent difficulty level.
The arena ladder doesn't give much incentive to compete either, with its meager monetary rewards, but it offers a quick combat fix. There are a few local multiplayer modes, but given the audience for this title, it would've been nice if the last PlayStation 2 entry in the series finally bothered to include some online functionality.
The reason devotees love Armored Core is its incredible degree of customization. You can swap out over 200 bits of equipment - heads, arms, torsos, legs, guns, missiles, rocket launchers, energy blades, etc. - 'til your thumbs bleed, and nearly all are available right from the start. It all comes to feel hollow, though: the missions aren't interesting enough to warrant the time and effort. Some of them even require certain loadouts to have a chance at success, though most briefings won't bother to let you know.
Armored Core: Last Raven isn't a broken game, and it's actually one of the better titles in the series - it's just that this series has been tragically underwhelming for years now. Fans will probably find it enjoyable, with its myriad robot parts and reams of backstory. If all you care about is getting some walking tank action, fine - but don't expect to remember it in the morning.