SpellTower is one of the most neatly designed word-puzzle games I've seen. Similar to Boggle or Scramble With Friends, it asks you to find words among a grid of lettered tiles. You can trace over letters horizontally, vertically, or diagonally, and even overlap the path that you trace.
What sets this game apart from others in the genre is that it also pulls in elements from the popular gem-matching game Bejeweled. For instance, once you find a word on the board, those tiles disappear (just like matching gems do in Bejeweled), causing the remaining tiles to drop down and occupy the newly vacated spaces on the board. Thus, the board keeps changing, which is an added challenge. To do really well in this game, you must think ahead and set up the board for higher-scoring moves down the road. It may seem a little complicated at first, but once you go through the clear and detailed tutorial, you'll get the hang of it in no time.
In SpellTower your primary objective is to score as many points as possible by finding as many high-value words as possible. Words must be at least three letters in length, and longer words are worth more. Words with five or more letters give you an added bonus and even cause adjacent letters to disappear, making it even more difficult to preplan moves. Other challenges include empty tiles, which are unusable, and blue tiles, which remove an entire row if used.
After the tutorial, you can only play Tower Mode, which is the most basic of the modes available. It gives you a 96-tile board (it says 150, but I counted 96) on which you have to find as many high-value words as you can. There is no time limit. As you use up your tiles, they won't be replaced, though, so the point here is to thoroughly think through your options and try to find the best words possible.
Once you play Tower Mode, you'll be able to unlock Puzzle Mode and Ex Puzzle Mode, both of which add an element of pressure to the game, as they insert a new row of tiles to the board each time you find a word. If your tiles reach the top of the board, the game is over. Finally, there's Rush Mode, which feels a bit like Tetris as it inserts tiles intermittently, as time passes. All of the different modes are addicting and challenging in their own unique ways.