You can get more back than you paid in - but this works only if you have the earned income credit.
Everyones W2s should be different from last year. There are two reasons for that.
(1) The easy reason to explain is that the tax was cut. Obviously the tax cut didn't help you at all, since you didn't pay taxes last year or this year. But that is one reason why you paid in less during the year.
(2) The second reason is harder to explain and doesn't apply to everyone. There isn't a simple formula like taking 10% out for each paycheck. The formula is much more complicated than that. The first couple hundred dollars don't have anything taken out. Any income earned after that is taxed at an accelerating rate. This accelerating rate isn't accelerating smoothly either (since some taxes like social security and medicare only are taxed on the first $80,000 or so income, so what you earn above that level has less taxes). This accelerating tax withholding means that if you are paid $500 and then $500, your employer will take out a lot less tax than if you got one check for $1000. How did this affect a lot of people? Last year had 53 business weeks, which happens every 7 years. Suppose you are supposed to be paid $52000 per year - which is usually paid out $1000 per month. If your employeer was smart, s/he would have noticed that last year had 53 paychecks, so you should have been paid $981.13 each week for you to still earn the $52000 salary. If your employeer wasn't smart, s/he would have paid 53 checks for $1000 each resulting in the employees earning $1000 more than the contract said. What does this have to do with tax withholdings? Like I said the amount withheld isn't linear, so with different earnings per paycheck, the withholding is not the same.