T4 is actually my favorite Traveller, and I was very unhappy when it was cancelled.
A version I'm not really familiar with, but the things I've heard...cheers!
An early victim of internet fan rage. But there were some spectacular failures like the first printing of First Survey and the equations in Fire, Fusion, and Steel.
But it does a good job of character creation. It's basically CT with four skills per term and education options. There is this one flaw though, aging isn't bad enough to deter anyone because at four skills per term, attribute boosts can easily keep up with aging losses. Anyhow too many people cheat on aging rolls. That's why my Galaxies In Shadow rules made aging absolute.
The basic starship creation is clean and quick and starship combat works well enough. Personal combat is a bit wonky and giving out 6d armour when most weapons only do 3d or 4d is not the best idea. Rolling the armour or just multiplying by 3 or 4 helps here. The dicepools for things are roughly equivalent to weakend blows and so forth in CT. World generation is world generation. Trade, geeze, I don't even remember but it's probably just a tweaked CT.
Anyhow, the supplements were a mixed bag, Emperor's Arsenal, Pocket Empires, Central Supply Catalog, the hardback combined Mileau Zero / Second Survey, Aliens Archive, and Psionic Institutes are all pretty good. Starships has a lot of flaws and errors in the advanced starship creation rules but at leasst the larger images make the ship illustrations a bit better. Fire Fusion and Steel is really pretty good but it's got fourteen pages of errata and the printer screwed up everylast equation in the book and it's a book full of equations. Emperor's vehicles has no usable game stats at all for anything, just vague descriptors and a chart in the back giving ranges of values tied to the terms. Imperial Starfleets is the rules to Fifth Frontier War and Dark Nebula without counters, or other usable information. I really never quite got how they expected you to use it. Mileau Zero is dull, okay? I'm sorry, it's just a bit boring. The first printing of First Survey messed up all the UWPs somehow. The idea was that there was a set for the players that just gave the phsyical details and a set for the referee that gave the full values. Fun way to do exploration right. Except I'm pretty sure they just printed the player's list twice. I only got the second printing.
The art well, the Elmore pieces in the core are decent enough if nothing too special. The Chris Foss art probably wasn't the greatest idea. I don't know, they're all lovely pieces but the black and white ship images in the core book are too small and dark. And some of the ships are pretty fanciful for Traveller's pragmatic aesthetic. The guy who did Emperor's Vehicles and Emperor's arsenal is decent enough, but he draws people with big heads. So there's that.
I think the biggest complaints people had were the nd6 roll under task system, the entirely necessary half dice therein, the art, the errors, and perhaps, the huge expectations of promises made and broken. Even so, I really think a cleaned up 2.5 could have dealt with some of that. Personally I was just happy to have Traveller back.