If you do the unity tutorials on youtube which are very good you will see how a very simple game is put together and how much work it will take. You will also see that there are many different programming languages that can be used to get to your end result.

Gamesalad may be easier to learn for you so you may want to take a look at that platform 1st.

I am also glad you said you wanted to create a tetris-like game and not a first person shooter right off the bat like others I have seen. I suggest watching all the unity introduction tutorials 1st without taking any notes or following along with the unity trial software- Just watch and observe the 1st time around- if you think its alot of work (and it will be) then you can save your money to buy the next version of MOH instead!! IF you decide the continue you should also start learning a programming language which will be of huge assistance later on if you choose game design as a career or another computer related field. WHen you learn one programming language, it can help you learn another since many of them share similar commands..., its like learning French and then Spanish- different languages but the "core" is similar enough that its easier to learn.