It's an enjoyable combat sim once you get to know the controls.
You see, the PSP's lack of a secondary analog stick is at fault as it is with the game's harshness. Game developers expects you to play it as if you have a full set of buttons, triggers, and 2 a-sticks. It's a God-given right that you'll be able to remap controls to your liking. But be prepared to lose some move commands, one or two perhaps. If you think you could overlook this problem, then good for you.
AC: Silent Line game's pacing is either easy or hard. It depends on your AC's customization. So there is a lot of trial and error during missions. But you might want to stick to one AC configurization once you've established your fighting pattern. Missions are pretty much standard. There are search and destroy missions, escort missions, etc. Although, it's basically destroying other enemy ACs. There is one stealth mission though but the variety of mission is not Silent Line's strongpoint. Earning mission rewards are hard though. The cost of ammo and repairs will deduct your the credits you earned in a mission. So if you keep on having low ap/ammo after missions then be prepared to have yourself in debt.
There's also Arena. It's a nice distraction if you like to get into fighting an AC right away. Aside from missions, this is the only way to earn money, and the easier way. You'll have trouble in acquiring money at first but it gets better once you're almost into mid-game. What's good is that you can sell parts/weapons you bought back at full price. Neat, huh?
As for the story, don't expect Silent Line to have a decent story, at least. It's too mundane and not much to look at. You're a mercenary, known as a Raven. You take jobs from 3 rival companies who are out to explore what's behind the ''silent'' line while choking at each other's throat. And the story's ending is a big disappointment for those who are looking for a grand ending. *SPOILER ALERT* *SPOILER ALERT* *SPOILER ALERT* You did your job. Well done. Let's ride back home. The End. *SPOILER ALERT* *SPOILER ALERT* *SPOILER ALERT*
As for the game's graphical and musical presentation, I would like to say they did a decent job. You have the limited option to choose what information will appear in your HUD. You could also change the HUD's color. The graphics are a notch better than Formula Front(my first AC game). It's an improvement worth comparing. The sounds are good but not that memorable.
As for replayability, you unlock extra arena once you rank first at the arena. Missions you have either taken or not will be made available post-game. There are lots of secret parts to collect. So if your a perfectionist, you might want to get A-rank(or S-rank? I haven't gotten one) in all missions.
All in all, Armored Core: Silent Line is a fairly enjoyable game once you get to know her. I said it before and I'll say it again. Just don't expect much about it. Enjoy.