Well we must put these battles in perspective and remember that hundreds of years separated them from one another. Yes, they were horrendous defeats, but they were many generations apart.
~We just have to remember that history is written by the victors. And the writings that have survived about the Roman army don't quote individual skirmishes and small fights. So we will never gain a clear picture. However, we do know the Romans were a disciplined army that conquered and held a republic (and then empire) together for hundreds of years. They fought countless wars in their time, and they won many victories as well as suffering horrendous defeats at time periods in their history. But to judge the legions we just have to judge the place of Rome in the world - which was the best place. The legions were disciplined, courageous and under good leadership from their centurions.
So while they weren't the invincible soldiers that TV often says they were, they were a tough army with a lot of skill, that forged an empire out of a small cluster of villages and held that empire together for many centuries.