Back then, molten armor was the strongest, Skeletron was the last boss. Based on the trailer, the physics were different in many ways, flails worked a bit differently, and tons of sprites and blocks were different (look at those smooth doors and shiny dungeons).
We're coming up on *six years* since the game released, if you can believe that, and updates are still coming. Here's a brief look at the game's history, discounting minor patches (though "minor" is getting hard to define with this game)...
1.1 came late the same year, with almost double the amount of stuff to do and build. Minor-ish changes rolled out, but a few months later Redigit said that development would be stopping on the game due to real-life issues.
BUT things change, and over a year later (September, 2013), 1.2 came giving us the crimson and beefing up what you could do in the jungle. Over 1.2's lifespan new events were added, and more and more items.
Then 1.3 in June 2015 (how has that been nearly two years?) brought us alien invaders, a new final boss, and expert mode, and extended the endgame even further. Tons of updates have come out in the 1.3 line, bringing new and refined mechanics, controller support, Mac and Linux support, new events based on other games, and more.
1.3.5 is coming "soon" and marks the return of Redigit to the development team. More info on that can be found here, but so far that information is sparse: http://terraria.gamepedia.com/Upcoming_features
That's not bad for a game that ended development 5 years ago! The thing is, I loved the game we had at the end of 1.1's update chain. When I found out that no more updates would be released, I was content. But the game we have now makes 1.1 seem quaint!