Warframe is that game I always wonder why more people don't talk about. For being an indie dev game, it is ridiculously high quality, quality that rivals Triple-A developers even. And it's free.
Terraria Community Forums
Xylia
neoselket
Is it an online game, or can it be played offline?
Xylia
Kinda-sorta both. The game is mostly an online game, that has an online lobby, however individual matches are hosted by players (and are local if you are going solo, which you can do). It's entirely free, no fees or anything required, however there is a paid currency system, but it is NOT required to play the game (and you can make this currency through non $$ methods)
Xylia
It can seem somewhat grindy at times, but the gameplay is very fast and fluid which some people dig. Will also point out that the servers keep track of your progress, so yes, it is online-required.
neoselket
But you can still play it if your internet isn't the best, right? Like, without ping?