While this is a high 2-star rating, Venetica is not particularly difficult. Only time consuming, as you will need two full playthroughs, plus an additional half playthrough. Also, the game has a reputation for crashing, which means you'll need to make manual saves at regular intervals, or risk losing your progress.

Expect roughly 30-40 hours for the Platinum.

Due to the good and bad endings, plus the three different guilds with their each set of quests, the game will require two and a half playthroughs. All your playthroughs can be done on Easy mode. There are a couple missable trophies which we recommend earning in your first playthrough, allowing a second chance in case you happen to miss them the first time around. Finally, be sure to make manual saves throughout the game, as Venetica has been known to crash at times, thereby losing your progress.

For your first playthrough, we recommend focusing on unlocking the Good ending for the Honorable Success trophy. Make sure to select at least the majority of any responses as a peaceful one, and select the Let Death take his Soul choice at the end. When it comes time to choose a guild, select the Order of the Holy Seal. Also, during this run, we recommend working towards the No Drugs trophy for completing the game without using any healing items, and the Quest Master trophy for completing 50 quests.

For your second playthrough, work on getting the bad ending for the Villainous Success trophy by making the un-peaceful responses, and select to slay Victor at the end. Also, use this playthrough to mop-up any remaining miscellaneous trophies you still need. Check out the Venetica trophy guide links in our Links page to see what you still need and their requirements. When it's time to choose a guild, first make a Save which you can reuse later, then select Net of the Mask.

Finally, for your third playthrough, load up the Save you made before selecting a guild, and this time choose the final Hooded Wings. Complete all the Hooded Wings quest, and provided that all other trophies have been unlocked, you should have the Platinum after completing the final Hooded Wings quest.

First, here's a detailed Walkthrough on GoGames:
http://gogames2010.blogspot.jp/2010/08/venetica-walthrough.html

And a Walkthrough on Venetica Wiki:
http://venetica.wikia.com/wiki/Walkthrough

paultsmith1980 has a great Trophy Guide here:
http://www.playstationtrophies.org/game/venetica/guide/

And a great Trophy Guide created by Pope Bodicius I:
http://ps3trophies.com/forums/showwiki.php?title=PS3-Trophy-Guides:Venetica-Trophy-Guide

zadorvp created a useful Trophy Guide here:
https://psnprofiles.com/guide/2816-venetica-trophy-guide

A great Trophy Guide by Rorylfc:
http://ps3imports.org/forum/index.php?/topic/33-venetica-trophy-guide/

A simple but useful Trophy Guide on Venetica Wiki:
http://venetica.wikia.com/wiki/Achievement_Guide

A Treasure Locations Guide on Venetica Wiki:
http://venetica.wikia.com/wiki/Treasure_Maps

A useful list of Quests with Reputation Points, by paultsmith1980:
http://www.playstationtrophies.org/forum/venetica/87120-quests-give-reputation-points.html

And a list of all the Guild Quests by Pkoptzky, here:
http://www.playstationtrophies.org/forum/venetica/87883-guild-quests.html

Rooster Teeth has a video demonstration of the Stealth Master trophy here:
https://www.youtube.com/watch?v=bhcHzcdwOCk

A video demonstration of the Dark Views trophy by Rooster Teeth:
https://www.youtube.com/watch?v=GXMPKq8vpdM

And a video demonstration of the Bright Views trophy by Rooster Teeth:
https://www.youtube.com/watch?v=GXMPKq8vpdM

Finally, here's a basic Trophy List:
https://www.exophase.com/game/venetica/trophies/