I heard that around release that this game has little content and that you had to partially grind to the cap. Does it have a lot more content now? Also, is the game fairly popular so I could easily find groups?

You've never had to grind to reach level cap.  There was simply a lack in the deviation of mission choices to reach it.

Anyway, yes there's heaps of new content.  The game is still niche, but has a strong communitry that is growing, and finding a group (if one wishes) isn't hard.

Do you kill cool things in this game? Like giant monsters or something? In WoW and many other MMOs I am tired of still fighting wolves and spiders when I am near the end game.

Yeah, there are several giant monsters to fight.  Some of them are bosses at the end of instances, but there are also several giant monsters that roam the world zones.   The most popular open world giant monsters are a T-Rex type dinosaur, a giant flaming ape, and a giant demon god shaman-looking dude.   They are one of the ways to earn high quality end game gear so it is popular for people to form groups to go find them and defeat them.