If you're playing against the CPU and you're button mashing, chances are it would be hard. The CPU 'learns' what moves you tend to use a lot and will use reversals with nearly psychic speed and accuracy. Some people think it's cheap, but it really isn't. If you become predictable, you will get reversed.
I thought it was cheap at first, then one time I was playing I stopped my combo short to see how Alpha 152 (the boss) would react. She whiffed a reversal, guessing how I would complete my combo. So it's not cheap, it just makes it very difficult to use the same techniques over and over.
DOA is one big Rock-Paper-Scissors game--moreso than most other fighters. If you keep doing Rock attacks, you'll be Papered into oblivion. Mix it up with a Scissors or a Paper however, and you stand a better chance of surviving.