Magicka is brilliant with other people - the glory of 'accidental' friendly-fire incidents, the joy of sheer overkill... seriously, it's worth the $2.50, especially if you can head online.
Memorizing combinations becomes a lot easier when you realize that the bulk of the spells are based on a simple formula. Each type has a 'style' of attack - lightning has a arcing cone, fire and water both have flamethrowers (waterthrowers?), arcane and life have beams, etc. The element with the highest priority (arcane > fire, for instance) determines what style of spell you cast. Beyond that, the other elements just make the spell stronger, and change its element - if you're facing an enormous tree, throwing a few fire elements into the mix will help.
True, the 'proper' Magicks require you to memorize spell formulas... but even then, there are only a couple of day-to-day spells that you need (Revive, Haste), and you can pull up a list of known Magicks at will. Heck, you can display your favourite right on your character, which is great for learning a new one! And once you cast them a few times, you'll memorize them naturally in no time.
In short? Buy it.
In long? Buuuuuuuuuuyyyyyyyyyyyy iiiiiiiiiiiiitttt.