The adaptation is pretty close so far, but you should still read the manga because there's no way in hell they're going to cover everything in 25 episodes. Also, precisely because of all the foreshadowing in the story, knowing what happens later makes certain scenes really interesting to (re)watch in the anime :V
One caveat is that the art in the manga is really rough and a bit hard to follow. It's not bad by any means, but it gets really hard to tell characters apart at times. The first time through, I didn't even realize Christa and Ymir were in the training camp arc.