A lot of it is just visual, TTS is essentially a 3d physics sim which places a virtual table (literally) in front of you. But to say it was just a 3d tabletop would be doing it a disservice.
All players can interact with the objects on the table, physically picking them up and moving them around (though they can be locked in place easily). It's mostly oriented towards the board game and RPG community but it wouldn't take much to use it very effectively for skirmish war games like Malifaux.
The main advantage it has over Vassal it that it's a step closer to physically playing the game. Being able to physically pick up and move your pieces feels great, it's a pretty slick interface that's easy to learn and has some powerful functionality built in. It handles decks of cards great, single click to pickup a card, hold to pickup the deck, shake your cursor while holding the deck to shuffle, rotate with the mousewheel or flip a card by pushing 'F'.
It's not quite as precise as I remember Vassal being, you can't step your pieces along inch by inch or display a range circle around a model but you can measure a line just by holding tab and moving the cursor.
It's also fully integrated into the Steam Workshop and it's fairly easy to create your own content.
Even if not for Malifaux I'd recommend checking it out, it's early access at the moment so there should be more features to come before a 1.0 release.