Games in infinism and terminism end after level three so you get a small taste of the game and if you want games to keep lasting longer and to continue playing then you'd need to upgrade.
And syllogism levels end at level 9 but in the full version you get 30 levels.
And I think some technical stuff like the amount of locks and bombs changes in this version and the full version.
There is also an ad in the lite version at the bottom of the highscores board area. Which doesn't allow you to view the worldwide highscores for best combos, top accumulated and etc... So in the full version you get to see more stats from the leaderboards. (The ad is on top of where buttons normally are in the full version)
But other than that, it's like the full version, you can log in, get achievements, play all the modes etc...
So if you can handle every game ending at level 3 then your good to go ....you can't get highscores that way though