I have never really played the old AC games. My only experience is through AC4/4A. I loved those games, it was great to be able to pilot a mech that wasn't slow but also wasn't arcady. I S-ranked the missions and took out the other mechs in the "Arena", but after all that there wasn't much to do. The multiplayer was ok, but it resulted in strafing battles.
ACV seemed to have taken the opposite end of the gameplay experience. I'll start with gameplay: It plays close to how AC4/4a played. There's some differences but they aren't huge and it is easy to adapt to. The ACs are smaller. They are half the size of what they were in AC4/4a. This is due to the amount of urban combat you will be fighting. There is a noticeable emphasis now on how you take on enemies. It no longer becomes strafing battles, if you take on a ton of damage or your energy runs low, it's best to take cover somewhere. The large buildings help make it easy to duck into some alley and recover your energy.
Because of the urban combat, one addition seems to be the Scan Mode and recon units. There is no longer a minimap to find your enemy. You shoot a recon unit and enter Scan Mode in order to locate the enemy. This also allows you to "see" through buildings. This also puts emphasis on the "Operator" in PvP. The Operator sees a map of the territory and players on their team. The players will need to use the recon units to allow the Operator to gather more battlefield information and relay that to the team.
As far as the standard AC features: There's still a good amount of parts to use, but it seems to be tied to you Team Level(I'll go over that later). More parts are made available once you hit certain team levels. You also find parts in missions or get them as rewards. Customization is also still here and in great detail. If you're a solid emblem creator, you have a good variety of patterns and "brushes" to use. I actually prefer this type of creator as it requires some skill to create amazing decals/emblems.
Controls are pretty standard. There is no longer a left and right shoulder weapon. Instead it switches out to the weapons so there's a slight delay when switching. Boosting and overall speed have been slowed down and you can now jump-scale buildings.
Single Player: You still have about 90 missions total with about 9 story missions that can actually take a while to beat. It won't take long to beat them but the story missions are no joke and can take a while to S rank. The 80 or basically "kill target" missions, sometimes with targets being other "boss" ACs. There is no Arena so the AI AC fights are all in those order missions. The single player experience isn't great, but if you're a completionist, there are "scrap parts" in most missions to look for and collect, and there's also the challenge of S ranking missions.
Multiplayer: This is the bulk of the game. If this doesn't interest you, then rent the game. Before you even start you need to create or join a team. Joining an established team gives you access to a huge list available parts already. It also gives you access to other players that can help you coop those missions. There doesn't seem to be a huge focus on trading in the game. Money is easy to come by and so are most parts. But if you wanted to trade emblems/decals you can.
Modes: Conquest: this is probably the biggest addition to the series and why I think it is a step forward. This allows teams to capture territories on a map. There are lots of territories within regions of the map. The team with the highest Territory levels will show up as the leader of that region. Conquest battles are either invasion type of defense type. There's more detail on how this works in forums so I won't go into that. These are generally a mix of PvE and PvP. The overall system seems to work but there are quirks in trying to defend your territory, which hopefully is ironed out later on.
Mercenary: Players can put themselves up as mercenaries. Once you register, you become available for other players to be recruited. When you register, you'll be put in the AC test room until a job comes in. The job details are displayed and you are given the choice of taking the job or declining it. There is a merc rating that ranks you on how much money you have made. Mercs who want to climb the leaderboards need to be careful which missions they take. The pay generally isn't great and you'll end up losing money if you take on too much damage.
Free Battle: This is a pvp mode. You can do a quick match or choose a match type. There are team battles, FFA, and duels. Pretty straight forward and fun.
Mock Battles: Your team can setup mock battles for practice.
As far as the multiplayer experience, there is lots of stuff to do. And even if you're on your own, you can hire mercs to help you out. I do have some issues with the game. Graphically, it's ok. Everything is just so dark and drab and it makes it difficult to see detail in other players' ACs, but all that goes out the window when you start fighting. The support from Namco Bandai isn't that good compared to From Software's support of the JP version. The manual is 5 pages, which is ok if there were other "official" places we can go to for information, perhaps an in-game manual or an official forum. There is none of that here.
If you're in the EU region, you also may have a problem trying to get matches. It is sounding pretty empty there and we can only hope that NB can merge the non JP regions in the future.
As far as the NA region, the population seems to be fine. I have no problems getting merc jobs and you can get in on a good variety of missions that way. I'll also note that I didn't experience too much lag in the games. I see it here and there but its not common. The PS3 version also apparently suffers from FPS issues. I have not noticed it since it doesn't affect the overall gameplay. I also found this game loads up missions very fast. Even navigating through the menus and going into assembly was a quick load.
If you're a fan of the series I'd add another star on my rating. I knocked it on the SP experience being such a small part of this game and the lack of Arena. It's a good game overall but for the uninitiated it can be tough to get into.
EDIT 04/20/2012 I have to knock down a star in less than a month. If you are playing purely for Single player and a huge AC fan, then I'd keep the star there. For people looking to play Multiplayer in the Conquest or Free Battle, you may be disappointed. Defense missions require players to wait in a room for their territory to be attacked. There is nothing to do but change you're AC configuration and the wait is indefinite.
In Free battle and merc, you need to be on at the right time, otherwise there won't be anyone else on.
In addition to the above issues, there's also Namco Bandai. The japanese version of this game is already on 1.03 to fix various parts balances. For all other versions:
Thank you for contacting Namco Bandai's Customer Support Department.
We currently have no information regarding any upcoming updates for the North American release of Armored Core V at this time. This information will be posted on the official Armored Core V website and on our Facebook page if any new updates become available. Please keep checking them periodically for any new updates as they become available: [...]
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I'd still recommend the game in hopes that a larger community would mean greater leverage in getting NamcoBandai to do something, and better matchmaking for multiplayer.