Far easier than its prequel, this is actually a low 3-star rating. The campaign must be completed twice, plus some possible mopping-up using the chapter select. There are 10 online trophies, but these are much easier and quicker than the prequel, and don't require a boosting partner (though it always helps, of course).

Will take 30 or more hours to complete, depending on your FPS skills.

You will need to play the campaign twice: once to unlock Elite difficulty, and a second time on Elite. For your first playthrough, it doesn't matter which difficulty mode you select, as they will all unlock Elite after completion. So it's up to you if you wish to start things easy, or get a better warm-up for Elite.

There are a number of miscellaneous trophies you can unlock along the way, though it's not necessary to do so, as you can always use the chapter select later.

Once that's finished, you can now play through on the newly unlocked Elite difficulty mode. This is where the 3-star difficulty rating comes in, as Elite can prove to be quite challenging and frustrating at times. Just be patient, and refer to some of the walkthroughs in our Links page if you're struggling.

There's one last playthrough required, and that's completing the Co-op campaign. Rest assured, you don't need to play the entire game - only up to the end of Chapter 3, and can be done on any difficulty. If you don't have a friend to play with, then simply plug in a second controller and let it sit on the floor.

Any offline trophies you're still missing can be mopped-up via chapter select. Check out the Killzone 3 trophy guide links under our Links tab for specific details to what you're missing.

Last, are the 10 online trophies. As we mentioned earlier, these aren't nearly as difficult nor time consuming as Killzone 2, and in fact can be achieved legitimately if you want, without requiring a boosting partner.

vhayste created a great Walkthrough, here:
http://www.supercheats.com/guides/killzone-3

IGN has a useful Walkthrough, here:
http://www.ign.com/wikis/killzone-3/Walkthrough

Here's a great Trophy Guide with videos, by vhayste:
http://www.supercheats.com/guides/killzone-3/trophy-guide/

And another Trophy Guide with videos, this one by PowerPyx:
http://www.powerpyx.com/guides/killzone_3.html#never_there

yewjhin, Yoshi_Girl, TheFlyingToaster, and Wozamil have put together a great Trophy Guide here, which includes the DLC:
http://www.playstationtrophies.org/game/killzone-3/guide/

And a great Trophy Guide here, by tripledt:
http://ps3trophies.com/forums/showwiki.php?title=PS3-Trophy-Guides:Killzone-3-Trophy-Guide

Jeff Belote created a Trophy Guide, here:
http://www.playstationlifestyle.net/2011/03/03/killzone-3-trophy-guide/

If you're in need of a Boosting Partner, here's a Boosting Forum on PS3 Trophies:
http://www.playstationtrophies.org/forum/killzone-3-a/94624-trophy-boosting-thread-read-first-post.html

Finally, here's a basic Trophy List:
http://www.allps3trophies.com/retail-games/killzone-3-trophies.html

This is one of the few first-person shooter titles in which the offline trophies are just as challenging as the online. Playing the game on its hardest difficulty setting - Elite - can be arguably considered one of the toughest FPS games to clear.

With a boosting partner, this difficulty rating could be dropped to a 4-star, but reaching the top 1% is still very time consuming, and needs to be concentrated within one week. Even with a boosting buddy, this is certainly one difficult Platinum to obtain - but one to be proud of.

We recommend beginning your playthrough on Easy. For one thing, as long as you finish the game - regardless of the difficulty mode - you will still unlock Elite difficulty. Also, there are a number of trophies, such as completing all missions without dying for Untouchable, and several timed boss trophies, which can be challenging to accomplish on a higher difficulty mode. So, play through from beginning to end, doing your best not to die, try to unlock trophies related to the timed bosses, as well as work through getting the kill-related trophies nad finding intel along the way.

After that, you can mop up by replaying missions. You can replay ones you've died on, as well as ones you're missing intel or any other random trophies. After your mop-up run, you should have all the trophies except for Heroic Survivor and the online ones.

Next, load up a game on Elite difficulty and prepare for a challenging playthrough. If there's parts of the game that are overly frustrating, you can always use the Mission Select to complete them in any order.

After you completed Elite difficulty, then congratulate yourself on a job well done. No one considers that easy. Unfortunately, you still have the remaining 10 online trophies to unlock. If you can find two or three people to boost with, you can set up private matches and boost for reaching the top 1% for that week. This means, playing nearly every day for seven days. If you're not boosting, then you'll need some serious FPS skills to unlock these online trophies.

Good luck!

IGN has a useful Walkthrough, here:
http://www.ign.com/wikis/killzone-2/Walkthrough

And a Walkthrough here, by Andre Segers:
http://www.gamespot.com/articles/killzone-2-walkthrough/1100-6205187/

Ratchet12345 has a great Walkthrough, here:
http://www.gamefaqs.com/ps3/928377-killzone-2/faqs/56524

Here's a great Trophy Guide by Sarnath and mjc0961, which includes the DLC:
http://www.playstationtrophies.org/game/killzone-2/guide/

And a detailed Trophy Guide here, by trophybot:
http://ps3trophies.com/forums/showwiki.php?title=PS3-Trophy-Guides:Killzone-2-Trophy-Guide

And a useful Trophy Guide by Jeff Belote:
http://www.playstationlifestyle.net/2009/03/12/trophy-guide-killzone-2/

A simple but useful Trophy Guide here, by AndyBSG:
http://community.eu.playstation.com/t5/Killzone/Killzone-2-Trophy-Guide-amp-Tips/td-p/7681906

xstation360 has a video guide showing all the Intel and Symbol Locations:
https://www.youtube.com/watch?v=6qWJoR2L98s

And a video by PringlesForAidan, demonstrating the Barrel Of Death trophy:
https://www.youtube.com/watch?v=E9ry038Ghbs

And PringlesForAidan's video demonstrating the Dragonslayer trophy:
https://www.youtube.com/watch?v=hsI4IGLFMZ4

Here's a list of the Ribbon Requirements, posted by Savenger:
http://www.playstationtrophies.org/forum/killzone-2/15273-online-ribbon-requirements.html

For those online trophies, here's a Boosting Forum on PS3 Trophies:
http://www.playstationtrophies.org/forum/killzone-2/2636-trophy-boosting-thread-read-first-post.html

Finally, here's a basic Trophy List:
http://www.allps3trophies.com/retail-games/killzone-2-trophies.html