From the Steam Store page:
For its 10 year anniversary, Titan Quest will shine in new splendour. This Anniversary Edition combines both Titan Quest and Titan Quest Immortal Throne in one game, and has been given a massive overhaul for the ultimate ARPG experience.
Anniversary Edition update
Restored and improved multiplayer functionality, including new features like a built-in voice chat and NAT resolving for best multiplayer connectivity
Support for more resolutions, larger camera distance and scaleable UI size
Improved performance and general stability
Support for modders through new modding options and a fully integrated Steam Workshop
Complete balance rework with improvements to all Masteries, damage types, unique items and sets
Countless bug fixes and other improvements, including ten yearsβ worth of community fixes
Increased challenges and rewards for larger parties and on higher difficulty levels
Dozens of new heroes and bosses to encounter
Improved enemy and pet AI
Quality of life features like higher stack limits, quick item pickup, a larger stash and a speed setting
Reduced cheating with curbed exploits, removal of test items and mod comparison in multiplayer
Steam Friend Invites
Steam Achievements
Steam Trading Cards
2 Comments - Last post 2 minutes ago by Landhammer
2,020 Comments - Last post 23 minutes ago by darkray114
33 Comments - Last post 25 minutes ago by Atombomb2097
844 Comments - Last post 28 minutes ago by sensualshakti
24 Comments - Last post 3 hours ago by Chad78
337 Comments - Last post 5 hours ago by kbronct
1,342 Comments - Last post 11 hours ago by Tuxerito
10,340 Comments - Last post 4 minutes ago by s4k1s
5,680 Comments - Last post 9 minutes ago by Oppenh4imer
109 Comments - Last post 14 minutes ago by CommissarCiaphasCain
43 Comments - Last post 30 minutes ago by hbarkas
8,925 Comments - Last post 48 minutes ago by Fluffster
621 Comments - Last post 56 minutes ago by Metalhead8489
59 Comments - Last post 1 hour ago by TrevorGoodchild