Personally, I didn't experience any issues with the game. In fact, the only setback I suffered was that Magicka refused to run on my laptop using Intel's integrated GPU (which was recently sold off in favor of something more capable). Frustrated, I headed into the forums to discover numerous other players having various issues, other than what I was experiencing.
It took a little digging to find out that Magicka doesn't support integrated GPUs, and won't play on an Intel graphics engine at all. That didn't seem to make sense, given that the laptop could run StarCraft II and Torchlight. But a commenter correctly pointed out that larger developers have the time and money to extend testing to a larger variety of hardware. Small studios like Arrowhead don't have that luxury. Given that many mainstream laptops feature Intel integrated graphics already, it would seem that the exclusion would lock out a large chunk of potential customers.
There was also mention that Magicka uses Shader Model 3.0 (part of DirectX 9.0c), which can play havoc with older, mainstream integrated graphics. Many forum members weren't too pleased that the game wouldn't run on their laptops, despite the Diablo-like isometric viewpoint. But according to Anton Stenmark, lead programmer for Arrowhead Studios, the team actually chose to use deferred shading instead. This technique is currently being used in other games, including Battlefield 3, Crysis 2, both Dead Space games, and StarCraft II.
"We decided to use deferred shading as our primary rendering method after discussing the spells and effects we would use in Magicka," Stenmark says. "Deferred shading allows us to dynamically add and remove any number of light sources at any time. Deferred shading is theoretically possible to implement using Shader Model 2.0, but most cards that don’t support SM 3.0 would have horrid performance using this method."